I've read your other post Op and may have commented in terms of getting your fertility checked out.
I'm a solo mother (to be) by choice and will try and answer some of your questions.
"I worry that the child would feel different or isolated. In the UK are they allowed to know who the father is?" As previously said by another poster, you are encouraged by the Donor Conception Network to share the story with your child using age appropriate stories so they become familiar with their origin as well the nature of conception. You are obliged by law in the UK to use an ID release donor: when the child reaches 18 they will have access to identifiable information about them. Research available suggests that donor children are well adjusted and that they are no different from children in other families. Children were not distressed in cases where disclosure of their conception had taken place, some of the research conducted by Susan Golombok who specialises in this field. As for feeling different and isolated, as long as the children feel secure and loved by those around them, the route to parenthood and what a family is can be 'non conventional' and doesn't mean that the man/woman/married etc. is the only acceptable family structure to raise a child in.
"What is it like being on your own and pregnant and having the child handed to you with nobody to share it with? All these things worry me." I'm currently pregnant (21 weeks) and I share my joy with my family and friends who have been behind my decision 100%. I have also become a lot more self-reliant in general as a result of this process. Yes, I have moments of doubt bit it's more to do with some practicalities of the process rather than doubting my decision. You can have whoever you'd like present at birth (covid restrictions pending), you don't have to be alone and have your baby handed over to you 'alone'.
"Is it lonely? I would have some limited family support but I mean lonely in the sense of moments when they grow up or making decisions alone like which school etc?". I can't conment per as I'm not at that stage yet, however I will also have very limited family support and will do the majority of child-rearing on my own and be reliant on paid childcare. Making decisions is empowering: you decide how you want to parent and again talking through issues/concerns with your family/friends is another option if that's available to you.
I second listening to podcasts by Mel Johnson and her other material on YouTube/Facebook from the Stork and I. She is a single mother by choice. She discusses a lot the idea of a 'fairy tale' and societal expectations of marriage and children, and if we don't find that, what are our options as single females.
I'd been married but my marriage broke down aged 36. I subsequently dated 'like crazy'. I even had a 2 year on/off relationship with a man whom I'd met on a dating app, but despite being in love/having a strong connection we were at different stages of our lives and I wasn't prepared to compromise on motherhood (I was aged 38 at this point, he was younger and not ready). He is now one of my closest friends, one of my biggest supporters and we are on very good terms.
I'd found dating to be utterly soul-destroying, anxiety inducing and extremely stressful. All because I wasn't finding the relationship that I wanted and needed at that particular stage and was terrified that I would either settle for someone out of desperation or worse end up childless through passivity and fear. I'm extremely happy that things have worked out the way they have; I'm also extremely lucky that my IVF treatment was successful the first time round (aged 39 and I have several frozen embryos in the freezer). Prior to IVF, I had one unsuccessful round of IUI aged 38. Yes, the treatment was expensive but I was fortunate that it cost approximately £7,000 and is manageable to be repayed in installments.
I genuinely still think relationships can be wonderful, however at 38/39 I simply wasn't prepared to put myself through the ordeal of dating hell for a small possibility of meeting someone (again) who was at the right stage to have a family. The risk was too high for me, plus I was emotionally bankrupted by this stage to date.
Doing this alone has allowed me to regain agency over this issue in my life and I'm no longer waking up in tears wondering if I'd missed my chance. I absolutely would love to date again once I've settled in to motherhood and find a partner that is right for me (not a pseudo-daddy for my child).
Nobody can guarantee that even if you do find a partner that the relationship will survive, you'd conceive, that they will be a good parent and that you'll get your happy ending. Only retrospectively can people say 'I knew he was the right one', but in reality it is impossible to predict whether a relationship will be successful or not, we can only speculate with the information we had at the time. For all those who did go on to meet a partner at the 11th hour, there are many stories of women who didn't and are childless through circumstance. They wouldn't be found on these forums, and are more likely to be found on Gateway Women a network for childless women (some women specifically wanted a family with a partner only and wouldn't have considered doing it alone). I did not want to give any man that much power. I did not want to be regretful because I was afraid to attempt this alone.
I didn't mean to high-jack your post Op, but I was where you were, and I hope my story provides a different perspective. PM if you have any further questions!