Hello & welcome. Based on my experience, what you are going to find is that sizes and fit vary from manufacturer to manufacturer. I am 5'7", 138#, 29in waist. Currently, I own an XXS from one brand that fits me as well as a S from another brand, while an XS from a 3rd brand is 4inches too short in the torso, and an XS from a 4th brand is a little too loose on the bottom. Measurements/sizing charts are helpful, but keep in mind not all fabrics stretch the same.
The only thing I can suggest is to find a brand you can try and if it fits, then seek THAT one out.
best of luck.
Small in Castelli. I should point out it is a San Remo suit, so may be different from the fit of their other skin- and speed-suits
Just a thought, so take it with a grain of salt, but you don't NEED a skinsuit. I'm all for looking pro and such, but a skinsuit isn't going to really impact your performance in a race compared to standard bibs and jersey you know fit you.
Personally I'd save the cash you might drop on a skinsuit and put it towards your next race entry fees this season. In my experience, once you try cross, you are hooked and want to do it again and again, even when you are in the middle of a race cursing yourself and saying "why the f am I doing this to myself?". You'll cross the finish line, take some deep breathes and a few sips of water and say "let's do it again". Whether or not you have a skinsuit on at the time will not change that reaction.