What to dress baby in in the summer

This is my seventh baby so I feel silly even asking, but every time I’m pregnant, I completely doubt myself and feel like a ftm all over again! I’m due August 14 but with my last two they came 2-3 weeks early, so I think my August baby could be a July baby. It gets hot where I live and we don’t have air conditioning in the house we just bought. Being in Germany, window AC isn’t even a thing and a portable AC costs over €1000 so idk if we’ll be able to get one. Last summer we all slept in undies and it was still hot. I know everything everywhere says to dress your baby in one more layer than you’re wearing but what if you’re sweating when you’re naked? Do I dress baby in a onesie or cotton sleeper or just a diaper? I don’t have any summer babies and our last house was much cooler in the summer, even without AC. An advice is appreciated, thanks 😊