As you have suspected, a fuzzy every 10 days is really not enough for your snake Yea for taking corrective measures!!!

Tanya had good advice when she suggested getting the snake onto an every-7-days feeding schedule. And your thought of offering an adult mouse is a good one. I don't know about your supplier, but I have one snake who eats live mice and I can't seem to ever get any that are over about 23g. Your snake will need one about 30g or a bit more (I'd suspect).

Double check your environment temps and make certain that the snake has an area warm enough for digestion (92-94F) and, like Tanya believes, your snake ought to start putting on weight and looking good!!!