Relaxing places

Perhaps make your down. There are nice beaches along the east coast of Terengganu. Perhentian or Redang perhaps.. 10 days is a long time in Langkawi.. Away from the beaches you can also head to Cameron highlands. Or the jungle Taman Negara..

Nothing wrong with Penang (if you haven't been there already).
Paul

Nothing wrong with Penang

except for the beaches.

There are some very quiet beaches on the east coast in Merang:
http://www.molon.de/galleries/Malaysia/EastCoast/Merang/

and as you can see from the pics, the sea water is reasonably clean.

OP wanted a place to relax and I think Penang fits that bill. OK the beaches are not so great.
Paul

Georgetown is not exactly a quiet, relaxing place. It's a city, with traffic and activity. Interesting to visit, but not a place where to relax.

you could get a ferry from Langkawi to the Thai island of Koh Lipe. You can get visas on arrival there and it's actually quicker to get there from Langkawi than from mainland Thailand. It's a small island with some amazing beaches!