I ordered an XL and I am 5 feet & 7 inches tall at 160 pounds.
It fit good and comfortable. Everything is meant to be a little loose which is accurate if you're cosplaying young David. Just be mindful on what size you order if you want something more fitted. The pants have a stretchy waistband portion along back which helped.
Only two negatives:
1) The chains and Cross were cheap looking. I would recommend getting something different. DokiDoki also sells a better-looking chain and Cross.
2) The collar is just a little too high in my opinion but it isn't a dealbreaker.
I also purchased the SR version but it wasn't going to arrive in time for Katsucon 2023, so I decided to purchased this R version to use in the meantime. It did not disappoint! The jacket, pants, and suspenders looked great with my chromed-up/upgraded David cosplay. Obviously, it is not the best quality as it is an R version, but it still looked great. Looking forward to the SR version.
Also, DokiDoki customer service is amazing! Thanks to their team for helping me change sizes after placing my order.