I would use a wool wrap under a sleepsuit at night, but usually DD wears longies at night with a top or whatever. Then il often use longies in the day with a top. sometimes they get pooped on so its good to have a spare pair of longies/wool wrap.
ive actually still got my original 3 vest extenders that i bought over 9 months ago! dont know how, i can never find one when i need it though! i bought a load of vests from tesco, cut the bottoms off and hemmed the raw edge to make a t-shirt which is great for using under tops when your child is wearing longies. i then sewed the poppers from them together to make homemade vest extenders for when she wears popper vests! much cheaper
id really recommend trying wool - its so excited having a custom pair knit for you, or you cann buy preloved or knit your own if youre on a budget
good luck! xx