I'm sorry to hear about your MMCs, such an awful thing to go through.
I had one last year and it has devastated me to the point of breaking my relationship.
My response has included....getting a puppy!
So I will tell you a bit about it. I have had a miniature dachshund for two weeks now so v early days. its hard work at certain times of day but it's been good for me up to now. He's a real lap dog if allowed to be and will go to anyone. It's a real testament to my breeders. He's slept through from day 1. I'm snuggling him now but the hard work to snuggle time ratio is stacked in the former's favour!
In your situation, I can see the upsides. Toilet training is pretty full on and would definitely take your mind of TTC. I took some time off work and did some working at home. I ended up really teary about my mc the day I went back because it was the first time I'd had space to think about it in a while.
If you proceed, I would think carefully about the breed. Maybe you want a small, lazy sod for when you get lucky and one that can walk at a pace besides the buggy. I think a cockapoo for example might be a bit much, they need a lot of walking and you're not going to have time for that, though maybe DH will.
Depending on your house, a dog that isn't given the run of the house and is crate trained maybe? This will mean dog will never have been used to following you round everywhere and will get used to entertaining himself for short periods. But hopefully your presence during maternity leave will allow him to build up tolerance for some alone time. They shouldn't be left alone the whole time of course but a degree of independence is no bad thing.
Your DH needs to be fully on board and be prepared to take the lead at certain times. My sister had an initial period of going off her JRT when she had her DS due to hormones, but they are good now. He also was walked a lot less as he was more her dog and her Dh is a lazy sod, even though he was the driving force behind the puppy. In fact, a lot of people thought a dog before baby was madness but he kept her sane during three years TTC. Yes it was challenging but they are through the other side. Her DS is great with my pup, he has no interest in handling him, he'll stroke him and play fetch with him but is largely cautious.
Lots for you to think about anyway, hopefully your house will be manic soon. I think the thing with a MC is it tends to make you grateful for it. Even if you don't go for it now, it can be something you promise yourself 'one day' which in itself is good as MC not great for giving you hope IME.
Good luck x