How tight do you like your jersey? I’m similar height and weight to you and usually go for large. I can fit into a medium but the fit is very tight and I find it restrictive when riding.
The returns is quite easy - the bag the stuff comes in reseals and you get a QR code to show the post office folk to pay postage. I wear medium and I’m 5 10 - you may find the bibs short.
How tight do you like your jersey? I’m similar height and weight to you and usually go for large. I can fit into a medium but the fit is very tight and I find it restrictive when riding.