There's quite a few places that sell the GDFB chausses. Having them tailored should be very easy, since they're laced, and not "tube" fit.
MedievalCollectibles.com sells some very cheap padded forearm / lower leg black padding. Like $15 cheap. I doubt it's high quality, but at $15, certainly would work to get started with, especially considering it would probably be under chausses anyway.
If you get mail chausses, it's also acceptable to cut off the excess in the back and lace them together with some leather cord. Early chausses didn't cover the entire leg, and were open in the back. That could be a good 'interim' point between getting them fully tailored and closed in.
Butted mail will work, and will lose rings. Riveted mail will lose rings too. The main difference is, all things equal, the riveted mail should lose less rings, less often. If you get butted, get galvanized steel, not aluminum - the aluminum is too soft and will stretch even more. Beyond that, they seem to really frown on aluminum mail for Days of Knights - even says so on the site/facebook.
Only other thing I can think of is to have a period drinking container.