I would recommend you head first to Belize...go diving for a few days. Fly to Tikal or you can catch a bus straight from Belize City to Flores which is very close to Tikal, getting to El Remate would be a bit better since its about 15 minutes from Tikal. After seeing the ruins (take 2 days to see Tikal, it can be done in 1 but its much nicer when you aren't in a rush) then catch a flight to Costa Rica via Flores-Guatemala-City-San Jose. Its not too expensive to fly from G'mala to CR. If you get stuck in G'mala City, head to Antigua for a day....beautiful old colonial city and very close by. I spent a month in Guatemala and always wanted to see more.
Once you get to Costa Rica I recommend you raft the Pacuare(close to San Jose), see Volcan Arenal(a few hours drive) and spend some time in one of the many rain forests; most people go to Monteverde(close to Arenal and a true cloud forest).
As far as renting a car, you wouldn't really need or want one in Belize or Guatemala but I highly recommend one for Costa Rica. Its quite safe and easy and pretty much every major car rental agency is in Costa Rica. Get something with 4 wheel drive since some of the roads, especially the roads to Monteverde are a bit bumpy.
In regards to a clean bed, you can find great little boutique hotels in Belize, Guatemala and Costa Rica. Guatemala is a bit less developed but in areas like Tikal there are nice little hotels and B&Bs. Very nice and very clean. You won't have any problems finding some place that suits you. Costa Rica has everything from small B&Bs to the Four Seasons...so take your pick.
Hope this helps. IF you need any other info please send me a message. I am sure you will have a great trip regardless of where you go. Just remember its not always about the destination, getting there is half the fun.
![Winking :wink: :wink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)