To ask my happily married baby daddy to donate sperm?

Conclusive argument right there. I expect you were never an equal and any hypothetical child fathered by your ex wouldn't be either.
Don't be closed the idea that you may in time meet someone who is perfect for you and go on to have children with them. You wouldn't want to be tethered to your ex in any way more than necessary. Exes are exes for a reason.

Ask him and his partner maybe suggest a 3 sum see what their thoughts are they could be keen.

I dont mean to sound insulting with this comment so please dont take it that way; but it sounds like you would benefit with talking to a proffesional regarding how you are feeling. Some really unsympathetic comments here. Yes it is no doubt a terrible idea what you are proposing but I feel there is more here influencing your thinking than just wanting another baby. The isolation and mental drain raising and caring for a child on your own day in day out can be debilitating to your mental health, especially in the Toddler ages as its so demanding time consuming it offers little opportunity for adult ineraction and socialisation. It sounds like you arent in a good place emotionally if you are having these extreme ideas. Some of the replies on here are disgraceful with how judgy and unsympathetic they are. I hope you find the support you need as it sounds like you are a fantastic loving Mum who has been put through the mill emotionally by your Son's father and its taken its toll on your mental health. You dont have to go through this alone. There is support out there if you need it.

And yet you want him to farther another child.

Your responses seem a little extreme.. you can have another baby without him being involved.
Id focus on him and yourself right now.

Honestly, if I was your ex partners wife , I would be furious if he agreed to this .

The new baby would still not have a Dad they are excited to see. He is still just a sperm donor

Lots of kids have sperm donor dads that actually wanted kids and then never make the effort to see them.

What worrying is this young woman probably expects the state to raise her kids.

Ask he might say yes, but fingers crossed he doesn’t.

Give yourself time. Your child still sounds very young but in a couple more years you may feel ready to date again.

You can't have everything you want. Both plans (ex or clinic) are insanely selfish, and 100% not in the interests of your current child, or your hypothetical one. If your ex is stupid enough to agree, it would (should) end his marriage and likely shatter his wife's life and mental health.

Please don't be true, please don't be true. I am not a snob but the use of the term baby daddy by you is already strange. Where I live I've only ever heard it used as a pejorative term to stereotype a certain type of parent who wouldn't be top of my list when choosing a mate.
You have a toddler. He didn't hang around long before marrying someone else. You say he's amazing but doesn't share care (50/50) of your existing DC (that you have almost 100%).
Even if any future DC was only his second child (I'd be pretty shocked if it was), have you given a moment's thought if something actually did happen to you. Is 'baby daddy' going to be their full time carer (and his DW) or is he just a sperm donor? You must be financially very secure not to need support for this second DC. Have you thought about this in any way beyond you own want for your DC to share DNA? This is honestly one of the worst posts I've ever read on here.

Didn't take long for the benefit bashing to start.

I don't think this would be a very good idea, OP

Arithmetic I imagine. The timescales sound pretty tight, adding another reason why this request would really not go down well at all.

🤣🤣🤣🤣

Just another day in this strange, strange world.

The biggest red flag here is your reason where you say you want the baby to have a dad. I don't think you understand the concept of a donor at all.

No no and no! This is totally crazy. You are asking him to be a dad not a sperm donar. They are 2 completely different things. You either go down a proper sperm donar route or accept you have 1 child.

having 2 children is so much more difficult than having 1. It's hard when there are 2 parents to help out, I can't imagine what it would be like when there's just 1 parent.

Plus the cost, childcare for example, plus everything else- clothes, toys, birthdays, holidays.

Can you afford 2 children on your own both financially and in terms of your time and energy?

Hes with another woman when you guys have a toddler together?

If this is real, and he jumped into a relationship that quickly, I’d say wait until they break up to ask!

How are you supporting your current child? Is he contributing financially at the moment - I hope you're not fully dependent on the state. Unless you're working and have the means to pay for childcare I don't think you should be thinking of having a second child on your own anyway. It's not fair for the taxpayer to have to fund your needs because you want a sibling for your toddler.

No.

Batshit idea.

Not least because he doesn’t sound like somebody who would fancy being on the hook for two lots of CMS.

not sure what you mean... what would happen to your child now if something happened to you? vs what would happen to your children if you had 2?

If I was your ex partner's wife I'd go bloody barmy at this suggestion
I guess if it were to happen youd try and involve him in the babies life..and that wouldn't go down well either.
If you have you child 100% of the time how are you going to have another baby ? You can't take the first child with you into the hospital. Have you thought about who will look after your first born while you are giving birth ,,?

My first thought

How will you support two children if looking after them full time ? I can’t imagine his wife would want him to commit to support another child .

This will cause upset in his marriage, and any civil or nice relationship you have with her. You shouldn't do this - at all.

If you feel really are going to go ahead anyway despite what everyones saying, speak with the wife first