30M, welcome to the board and to the Thailand branch.
Particularly at this time of year, I would recommend coming to the Andaman Sea side of the country for the best dive sites in Thailand and the most favorable sea conditions. You would fly in from Bangkok to Phuket or to Krabi.
If you are looking at two to three dives a day, you will probably want to do daytrip diving rather than a liveaboard, which typically schedule four dives per day. However, there is no rule that you have to do all four dives--you could still do a liveaboard and skip some of the dives, and you probably wouldn't be the only one aboard doing so (some people don't like to get up early and skip the first dive; some people don't like night diving and skip that one, etc.)
In terms of daytrips, from Phuket you would have the option of diving at the Similans, far off the coast to the north of Phuket Island, or of diving at the nearby islands to the south and southeast of Phuket. From Krabi, you can get daytrips west and south. From both places you can get overnight trips with lodging on Phi Phi.
In terms of liveaboards, it may depend more on your level of proficiency and experience whether that would be a good option for you. If you are a brand-new diver, you might want to wait until you are a little more experienced to undertake that sort of intensive dive adventure, but it certainly does depend on the individual!