Quoting Crystal Marie S.:" He would need to be pretty hot for brain damage to occur. Did you happen to take his temp? A lot of ... [snip!] ... wearing a long sleeve shirt pants and socks, LO should too. If it's hot and you're wearing a tank top and shorts, so should LO."
One of my biggest concerns was letting him get too cold or too hot. When it's cold here, we put the heater on low (we have a electric space heater). I dress the baby in a sleeper and put a light blanket over him (tucked under his armpits into the bassinet) and then I lay a thicker blanket over his legs. If I wake up and I'm hot, I check on him to see how he feels. Or if I'm too cold, I'll bring the thicker blanket up to his armpits.
Babies will usually cry if they're hot or too nipply.