Twice has free shipping on orders over $50, and I usually don't have a hard time managing that even if I end up returning some of it it saves me $. It's the first place I've regularly bought from secondhand online - I've never been an ebayer, it's not usually worth the bother for me. I tend to go with trusted brands / companies online, because I know how they tend to fit me and what sizes I probably am, not to mention return policies etc.
Shiny, it sounds like you need to shop, or rather, you need new clothes, but you just don't feel like shopping right now with everything else going on. Is there any way you could get someone else to do the shopping for you, or at least do a lot of the setup & research? Maybe a personal shopper from a department store or someone who does it independently?
On a more meta note, I find that this kind of thing can be optimized infinitely, but it's not always worth your time or energy - in other words, there's always more reviews to read, more money-saving strategies, etc. But it tends to follow the 80/20 principle - there are some quick fixes so you don't waste time and/or money, but pretty quickly your returns start diminishing while your time keeps getting used up. You mention redirecting anxiety and I do that myself - I'm stressed about something else that's not entirely under my control and so I fixate on something I feel like I can control, like shopping. It's a coping strategy but it doesn't mean there's actually anything horribly wrong with my (your?) shopping process either.