Unfortunately there are not too many places to visit in peninsular Malaysia that are that interesting. I've been too many times and have, frankly, run out of places to visit (and it didn't take very long). East coast is better for getting out to the islands if you are interested in diving and snorkelling. There are some interesting drives through the rain forests (particularly one places where Malaysian aboriginals were selling the ripest and freshly-picked jack fruit (there's a national park but that would involve hiking with all the usual stuff such as insects and leeches). Mostly, it seems to revolve around the food, and that takes some research.

I have also just learned a trick about buying shorter distance tickets for the long-distance (ETS) trains in advance: Try adding stops further up or down if KTMB isn't offering tickets as "short" distance (e.g., Ipoh-Butterworth) tickets are not sold more than 24 hrs in advance.

You could also consider ride share for the shorter haul road trips. Grab (good for taxis too) is the pre-eminent one followed by Tune (Air Asia) and Maxim though the latter appears to be primarily in east Malaysia.