Seasons hot and cold weather clothing tags - is this all that's available?

Nope, you are not mistaken; there are very limited options to choose from if you have just the basegame. The categories were technically made with only Seasons in mind so you'll have a few more options but even they don't provide enough options imo. With other packs some clothes from there will be tagged for Hot/Cold but even then, honestly there still aren't enough choices to choose from. I say save yourself the trouble and remove the tag and just pick what you think is appropriately hot/cold for your sims.