I would find a dressage trainer asap who has 4th level/GP school masters for you to take lessons on. Before I found my OTTB, I thought I wanted to buy a well schooled dressage horse so I took a few lessons on a GP horse an hour away from my town, and even though I pretty much sucked at riding that thing, I got the feel for how a correct dressage horse was supposed to ride, and how to ask for basic aids. So to answer your question "what can I do on my own", do some serious web surfing for trainers!
And coming from a very practical point of view, do you feel comfortable (after you suggested you weren't very fond of dressage) refreshing a 4th level horse right off the bat coming back into serious riding? I'm not trying to challenge you, I'm just curious because I feel like your level of confidence will especially be a big factor in your success in your situation.