Any man who envisions himself as a woman sometimes probably has a clear idea about what kind of woman he wants to be and how will she look like. And that is great because you need some guidance in order to get the right look as close as possible to your fantasy, right? So, you know how you will want to dress, what kind of shoes you’ll have, the right hair… and yes, what kind of beautiful cleavage you will have, wink*
Now, one advantage that you as a cross dresser will have is you can choose and change your breast size as you wish, lucky you. A would advice you to choose a breast form proportional to your height and weight, but if your fantasy involves being incredibly voluptuous, then by all means, do it. But keep in mind if you are going out in public, you might attract some curious glances.
Get some measuring tape and measure your chest about 2.5 inches bellow your nipple. That will be your band size (they usually run from 34 to 44 and more); about the cup, keep in mind if you want smaller breasts, anything from a B to a C cup padding will be on the petite/average spectrum, D to DDD will be voluptuous. But once again, these are measures so you can have an idea because it will depend on your overall size to see how it looks. For instance, a 6’2 guy who weighs 200 pounds might look totally proportionate in a D padding, but a 5’5, 130 pounds man will definitely not look proportionate in a cup D. Get what I mean?
Once you have figured out what size you want to get and have gotten your perfect breasts padding, it’s time for the fun part: bra shopping. I don’t need to tell you they can be found in virtually any design and fabric, so you can choose whatever you like the most: leather, lace, silk, strapless, bralette, underwire, no underwire, balconette, etc… sexy lingerie sets also apply (my favorite ones are lace, but hey, I know you love leather wink*) When you get your new breasts you can either stick up with that size or have several of them and rotate them to change your look (and your play?). I mean, maybe bombshell Lucy has huge DD knock outs that she loves to display in sexy dresses while she dominates you… But shy Nancy has demure B cups and is oh so surprised that you want to get your wicked way with her…