Be very very careful.

KUL really feels like two airports: KLIA1 and KLIA2. They are right next to one another, but getting between them isn't like changing between LHR T3 and T5: You have to exit immigration entirely, go get some Malaysian ringgit, and pay 37p per person (MYR 2) for a bus that takes you to the other airport.

https://www.tripadvisor.com/Travel-g...And.Klia2.html has some more information.

Air Asia X flies out of KLIA2. BA and Malaysian use KLIA1.

The Malaysian Airlines connection will be the /less/ tight connection for you. I would not do the Air Asia flight unless you had >3 hours to connect.