Hi Joyce.
I had the same dilemma before going and took far too much in the end.
I pretty much wore Shorts and vest tops during the days (both in the town's and jungle), it's was hot and humid, so I went for what would be cool and comfortable. As long as you cover yourself we with deet, you shouldn't have too much of a issue with mossies. They got me a couple of times but only when I had missed areas or hadn't re-applied enough. (I found boots deet wipes easy to use and apply while out and about) Evening were much the same, staying cool. There is no real need to get dressed up at all, I went for mainly linen trousers or cropped trousers with sleevless/vest tops. Shoes - I pretty much lived in flip flops or walking candles, even getting on and off the boats that was fine. (again make sure you deet your feet!) Make sure you do have a pair of closed toes shoes though - needed when you go tree planting as it can be quite muddy. I took my walking boots and they never came out of my bag.
I hope that's of some help and hope you have a fantastic time. I certainly did.
Paula