Makes sense needing to replace BM with formula.
To clarify, there is no need to use formula unless you want to switch BF to formula before 12 months. If you are happy to BF to 12 months then at 12 months you can switch to cows milk. There will be a period of adjustment of course.
At 12 months if you switch to cows milk it needs to be whole milk (or full fat as some people say) not semi-skimmed or skimmed, and this continues until LO is around 2yo (I believe from memory at 2yo they can switch to semi-skimmed or half fat if solids intake is good, I have never switched my DS he still has full fat milk daily).
Whilst some LOs might initially refuse cow's milk some will just take it. Mine was formula fed and at 11.5 months I could not get any of his regular formula anywhere in our town, I decided to give whole cows milk at that point and he just took it, it was a little early but I was comfortable with it and he didn't bat an eye at the change.
So instead of feeding him after the pm nap would I move straight to dinner? What would a good feeding schedule look like for 3 meals a day plus milk feeds?
I find the easiest routine is to keep milks in place and put in solids an hour later:
7.30 WU BF
8.30 solids breakfast (he can guide on quantity, introduce some finger foods too)
11.30/12 BF (not now but later this becomes snack)
1.00 solids lunch (he can guide on quantity, also offer finger foods)
4.00 BF (not now but later this becomes snack)
5.00 solids dinner (he can guide on quantity, also offer finger foods)
BT BF
TBH 5pm is a little late for many LOs to have a solids dinner, it's on the edge of being ok but you might find a touch earlier is better, especially as he gets older, for now it's fine and may well turn out to be fine later on also but many like to eat their evening meal pretty early, 4pm-4.30pm ish, it's not a rule though.
I generally shy away from offering BF advice because I was unable to BF. I believe 1 NF would be usual at this age (but some choose to continue more and that is personal choice).
I would begin now to let him have his fill on solids by following his cues to fullness/interest, offer finger foods too. This may well begin to pave the way to dropping those night feeds. Make sure to offer some high fat and protein foods, meat, fish, cheese, as well as veggies and carbs.
I'd suggest a thread on the BF board for support in dropping the NFs and re-settling at night wakes instead. I can ask a BF mod to pop in here but you're unlikely to get the overall support available from the wider community if I do that.