Hi Maggie, I'm also on that trip and looking forward to it. My last planned trip to Costa Rica was cancelled due to Covid but I was determined to get there eventually. Make sure you are up to date with your jabs and take suncream and Deet based mosquito spray. Take a couple of cool lomg sleeved tops and trousers, and lightweight trainers to help protect against insect bites when we are in the rainforest (or spray liberally with mozzie spray) and a packable waterproof as the rain showers can be intense. Sandals and cool clothing at other times. Don't overdo the evening wear! Try and have the air con on in your hotel room at night to keep it cool and dry, dont' worry about mosquito nets.
Tips from other travellers always welcome.
Look forward to meeting you on the 15th,
Valerie