So I received a job offer but I would like to wait a couple of more months to check the market and apply to other jobs. I'm just starting my job search, I'm not in a hurry and I would like to take the time to check other opportunities.

What's the best way to deny a job offer without closing the door, in other words, so that if I don't find anything better in 1-3 months I can perhaps accept the job if of course they are still interested?

Saying "Thanks, but I want to look for something better first does not sound good :)