Oh gosh. What a tough year. I'd like to say well done to you for coping so well this far.
I have three kids, have empolyed several live in nannies along the way, and now have an au pair / childminder combination (mostly for the purpose of pratically eliminating my tax obligation). My children are 9, 7, and almost 2.
Some things I think you might want to think about:
Do you want a live in? If you have the space it sounds like you might like the flexibility (e.g. early starts) of a live-in employee. And, as you are on your own, you might even enjoy the adult conversation at the end of the day. My DH often works away and sometimes the nanny and I will hang out in the evening, watch a movie, talk about the kids, have a curry, etc. I am a social being and I like having another person around. But, some people prefer not to have another person living in their house.
Have you considered a combination of an au pair and keeping the daytime childcare (nursery, childminder, etc.)? This will save you a huge amount in tax obligations whilst still giving you quite a bit of flexibility on the hours. But, it will require you do a bit more on the job training. So if you want someone to hit the ground running without your involvement then this option is probably not for you.
Think about the hours, the duties, etc. and tailor your intial ad / interview qustions to targeting those candidates. For example I am a fuss pot on nutrition, so my questions ask quite a lot about what the potential nanny likes to eat. My 9 year old has a quite a strong will, so I also look for someone with a strong personality and some experience of discipline because otherwise 9 year DD is likely to walk all over them.
In your case, I think you might want someone with some experience of sleep problems. That is one problem I have never had, so can't really advise there. But, I would probably put something like "experience with difficult sleepers would be a plus" in the ad.