Have stayed at Pangkor Laut but not recently. It's a traditional self-contained luxury beach resort, maybe not up there with a classic Aman, but it was a nice experience.

There is also a Shangri-La in Penang but it is more likely upscale than luxury and you have to pick your higher-end room properly to make sure it is upscale if my experience there isn't dated by now.

Found nothing even that I would call upscale in Malacca.