First of all, note that the Mercure is closed January 24 - February 6, as well as May 9 - June 6.

Secondly, the Mercure is often full, it essential to book as far ahead as you can.

I personally prefer the Mercure, but there is also the Yotel, which you can easily book online, usually for a reasonable €76 for 12 hours, which should suffice if you are spending one night.

Yep, the Mercure is airside, as is the Yotel. The fomer is opposite KL Crown Lounge 52, the latter adjacent to the Terminal 2 food court on the upper level on the D pier/concourse side.

Johan