I will tell you, Sir Nathan- and I'm sure others will back me on this, but your foundation garments are key. If they don't fit well, pretty much nothing else will since all of your measurements will stem from when you're wearing your undergarments. Seeing as you're still very young and new at the game, you may decide to make your way as many of us did- going with off the rack options for the sake of saving money; this isn't a hobby for the faint of heart or wallet!
Now, if you are so inclined you could consider making your own garments- thereby saving yourself a good deal of money by making your gambeson, tunic and pants, surcoat among other things that are textile in origin. I'm lazy, I'd rather buy it than make it but others, like Sirs Edward and Nathan seem to also be blessed with seamstress skills as they've made things that are way out of the realm of possibility for the likes of me; if you're like them then it is something to consider. The beauty of this game is that most of the players want to see others get to where they are so there's all sorts of patterns out there for clothing and other garment products as well as shields, armor and the like. Its always fun to try your hand at new stuff (unless you dislike that sort of thing then it isn't) and of course, feel free to ask questions...for how else are you to learn?