i use doggystyleclothing. they are uk based, the only draw back they can be a little slow with deliveries
i dress up for pics and special occasions, and if they are going out in the cold
I enjoy dressing them up if they need it. As long as they dont mind and its practical for movement/temp, etc then I dont see what is wrong with it.
I like doggystylestore for cheap basics and Elmo's Wardrobe for the pricier stuff.