Sounds amazing!
Easier said than done but try not to bring too many clothes; you'll only end up wearing the same few items, and you can buy most climate appropriate clothes out there.
My list would be:
A few loose tops, including ones with long sleeves to protect you from the sun and mosquitos.
Shorts, hiking trousers and a fleece or hoody that folds up small and dries quickly.
A pair of comfy leggings / harem pants / joggers for travelling days.
A lightweight rain Mac.
A lightweight big cotton scarf (I recommend The Mumsnet Scarf!). Can be used as a blanket on long bus journeys, rolled up as a pillow, as a sarong, a shawl, something to sit on on the beach - so versatile!
A microfibre towel because they don't take up much space (but they can feel quite horrible on your skin).
A light / medium impact sports bra or crop top; sometimes bus and taxi trips are super bumpy and you might need the extra support when travelling.
Comfortable swimwear that you can freely move in (e.g. not only a strapless bikini, you might be climbing in and out of boats etc.)
Try to bring one dress / nicer outfit in case you want to dress up slightly in a city one day. After a few days in the jungle even just having a shower and wearing a maxi dress will feel very fancy! Choose an outfit that is a crinkly or stretchy material so it will still look OK when it's been screwed up in your bag for weeks.
Are you planning to do a lot of hiking? Think about if you'll really need proper hiking boots (very heavy and take up space) or if you can get away with wearing hiking sandals instead.
The lush shampoo bar is useful and much easier to transport than a bottle; their conditioner bar wasn't very moisturising though. You can buy most toiletries over there and it'll save you using up your luggage weight allowance with heavy liquids. The only exception would be any make up you bring (if you wear it) but in some places the humidity would make it slide right off your face anyway so there's no need to bring lots.
Not S&B related but get some US dollars and hide two or three emergency stashes of ~$100 in your main bag, handbag and day pack. That way if one of your bags gets lost or stolen you will have enough for a room and food for a couple of days until you can access more. Also, scan a copy of your passport and email it to yourself and to a trusted person at home, along with your travel insurance information. It will make things easier if your passport is lost and you need to make a claim.
Hope you have a fabulous time!