"What can I use to make having sex in water more comfortable?"
I’m going on holiday to a hot country and our villa has a private pool. I want to try having sex in water but the last time I tried, it felt quite uncomfortable.
Pick up some silicone-based lubricant. It’s a bit more expensive than water-based lube but worth it because it won’t dissolve in water. Insert some yourself before you jump in and then get him to use short thrusts and hold you close to his body, rather than pulling most of the way out. That should block most of the water from getting inside you.
Another option: let him use his hands or put you on the side of the pool to deliver oral sex and save penetration until you’re out of the water.