First of all the wool longies - as long as they are 100% wool she will not get too hot. Wool is breathable so it is warm when you are cold but cooling when you are hot. PUL is plastic. It is not breathable so it is sweaty when you are warm. Lots of moms here put wool shorties on their babies in summer to keep them nice & cool. Wool needs to be lanolised to make a waterproof layer. Are you woolies lanolised do you think?
If the longies aren't 100% wool, they can be used like pul covers (wash after a wear or 2, wool only needs washing every couple of weeks or so).
Secondly, your dd is at the age where stuffing day nappies doesn't cut it anymore & many move on to dedicated night nappies. Weenotion night nappies are a good all rounder & are easy to get on classifieds here. Your dd is only leaking at the tummy because that is where her wet zone is & sleeping on her front, I wouldn't expect her to outwet the whole nappy as there is nothing to make the wet travel up to the back.
The other option is to use better inserts. you are using cotton & microfibre which are the worst absorbers. Try using a double bamboo insert with a hemp booster underneath. That is the best combination. Wool will also be a huge help as it allows some of the moisture to evaporate (because it is breathable) so the inserts will have to absorb less liquid.
Hope that helps