There are abundance of forest/jungle round Malaysia, and i dont think you as an adult should need the malaria pills.
a good insect repellent should do the job keeping the mosquito's away (purchase them when you arrive in Malaysia as these are localise mosquitoes, overseas repellent might not work as effective).
me being an avid hiker and trekker been round Malaysian Forrest for a bunch of times and not one of my friends and companions been diagnose for catching Malaria. so you should be OK.
A more common mosquito carried virus is the Dengue fever. it is carried by the Aedes mosquito, this is more common because it breeds around us in clear, still water and Malaysia being a developing country, there are plenty of places to breed.
Not that we leave the rubbish lying around to collect water (although some of of do), the major cause now is the development of of country with a lot of building projects on the way, with these mega projects, comes various pollution which includes water catchment for these aedes mosquito.
the only way to protect yourself, is through insect repellents.
Don't worry, Malaysian Health care is one of the best in the region, and you will be OK. and chance of you getting it is very very slim.
Anyways, Welcome to Malaysia!! and Selamat Datang!!