I love the Castelli climber’s jersey in the heat, lightest weight jersey I’ve worn. You can burn through it so sunscreen on your shoulders helps
For fit with Castelli it really depends on your build. For reference I’m 6’3", 170 lbs, and wear a medium bibs and medium jersey in Castelli - although I may size up to a large bibs next year as they changed the shoulder strap length this season
If you can find someone with a Castelli jersey you can figure out the size you would be