We had this dilemma OP. Happy in the nursery of a (n outstanding) Prep - chose to stay on for Reception and into Yr1.
DD is very young in her year - very bright but like a butterfly in terms of attention span back then.
It didn't work for a few reasons - YR1 demands in terms of homework (at barely 6 years old) just didn't sit well with me.
School was better in terms of before/after school care and I could work without worrying about any of that.
But we moved, to an outstanding Primary in Yr 1, because I found the Prep too pushy, I am not a hot house type and think that education is a marathon not a sprint.
I wanted my child to be a child after school and not to have to do 20-30 mins of homework a night, plus reading back then.
I had to give up work in the end due to lack of after school care, but it isn't forever and we don't have any fees to pay for another couple of years.
If I had a naturally studious child I would probably have stayed (or if the school had been a better fit) but I didn't. Absolutely the right decision for us, she is working ahead in a lot of areas 3 years on, without the Prep style homework.