I would never ride without a chamois now either! And it doesn't matter how long the ride it is just more compfy period! i am afraid I can't help out with size. I wear a med in everything. But I don't like how some of the mtb (mountain bike shorts) fit. I have sporty thighs (I like that, instead of big) the the legs in the mtb shorts bind. I like the fredom of the lycra. But I have three pairs of mtb shorts now that don't get used! The bike shirts are good cause they tend to be longer inthe back, that way you don't get sun burnt. also a big floppy shirt is not good in a wind. Welcome by the way to the world of biking! And to this site. This is the best one out there (not very many for women) you can pretty much get advice on anything. Just check open topic. Hope we are of some help!