I bought my first bra from a charity shop. It was really orgasmic to ask the lady, "can I try it on!"
Since then, I have found that bra sizing is a difficult business: bras which initially seem too tight in cup, band and strap can become lovely & supportive to wear when broken in.
I now buy most of my bras through eBay auctions. I can often buy new bras for not much more than the postage cost, and I can experiment with sizing too. Buying used bras is fun as well: they are very cheap and you know that someone else's boobs have been in those cups!
For a sizing example, I am nominally a 40" band, and I have found that 38" bras with deep side panels & a 3 hook deep back band take my breath away on initial hook-up but give me really snug support and wicked cleavage.
Basically if my bra gives me lots of projection, I soon forget how uncomfortable it is at first wear!
I buy a full cup bra in one cup size too large if I plan to wear it in public with my Nipplefunwear nipple teats, and I look for a demi cup plunge bra to wear indoors when I am using my electric breast pumps, so that I can support the pump nicely in my bra cup.
The next items are the colors and strap buckles. I love to wear a bra which is only just obvious from its color,the print of its straps and the bust projection. I love to hear women remark: "I'm sure he is he wearing a bra, but did you see those nipples?"