Only answering part of your post, but milk in Thailand is just fine. There are 7/11, Family Mart and other such shops literally all over the place (I swear that there are 7/11 shops next door to each other here!).
Most of these will have full fat, many will have skimmed and occasionally some will have semi skimmed.
Go to a bigger supermarket (Big C or Tesco Lotus) and you'll find just as much as you will back home.