Hi
The coined terms of "adult products" are too vague to convey anything significant. I'd suggest you to provide an exhaustive list of items that you intend to trade in.
You need not present the list to me. The point is that, by compiling the list, you will have a clear idea of what you intend to sell. Furthermore, if you have any doubts in the future, you can always ask the relevant governmental bodies or agencies in Malaysia for clarification.
I'm convinced that they will ask you, "What are you actually selling? Could you name them?"
FYI, Malaysia has yet to become an official Islamic country. Yet, the status quo doesn't prevent the Malaysian society and the relevant governmental agencies to clamp down on your business.
Condoms should be OK. I'm sure you've come across condoms being sold at pharmacies and convenient stores in Malaysia.
Costumes too should not cause you any problems.
Sex toys though are a different thing altogether.
Basically, if you're going to sell dildos, artificial ######s, vibrators, cock rings, anal beads, etc, you will very likely encounter problems as you go about operating your business.
Consult your lawyers, those Islamic governmental agencies, et al should you feel the need to have confirmed answers to any of your questions.
Good luck with the new business!