I'm between a 48 and a 50, and I can tell you from experience that while his outerwear tends to run TTS or slim, his knits are generally oversized. Check out his shows - in many cases, the knitwear is worn over outerwear...
There are also belts made for the Japanese market, and these bolero/armor things, as well as tons of tees, besides what I've already mentioned.
I have like 20 Geller pieces, so I know how it fits
Im a 50, Geller 50 in outerwear works perfectly, knits could still be an option and maybe T's too
I've got like 12 pieces of Geller outerwear, so honestly I don't think I need anymore
Would like a few more knits though, and some T's, was hoping for some of the older jewelry too