I'm in Singapore so it's summer all year round here
We're somewhat acclimatised after 2 years but I put C in a sleeveless or short sleeved bodysuit inside a 1 tog sleeping bag. If it's way hotter than usual I'd probably even skip the onsie and just put him in a nappy inside the bag, no other bedding.
Callum is only 6mo so no iceblocks here

But he is really into sucking on icecubes in muslin at the moment for his teeth but they are a decent size and he has a couple a day - just a bit extra fluid, it all helps! If iceblock moulds are cheap there's no harm in trying them, you will use them next summer for sure. You can make ice blocks with pureed fruit and 100% juice, they're pretty popular with older kids I know!
No cloth nappies here sorry, so can't help with that one.
Enjoy the heatwave!