I once tried forms, very expensive ones, but I found them uncomfortable to wear all the time. I think I wore them several times when I went out to a club or something before going full-time. I then started hormones a couple of months later and found they were even more uncomfortable with growth going on. Pre-hormones I was a little under an A cup, like an AA. I wasn't over weight or anything, I just got developed them in my teens for some reason.
But, anyway, my point is that before you spend money on forms, think about how often you will wear them and when/if you are going to go the HRT route.
Bigger breasts don't always mean better, as well. B cups are pretty nice. I completely fill a B cup right now and I haven't stopped growing. Although, IMHO, breast size doesn't make or break a woman.
So, anyway, things to consider:
1. How often are you going to wear them. If it's all the time, you might want something that's as comfortable as you can get in a budget that you can afford. Wearing breast forms can get uncomfortable during the day, especially if they have any weight to them, and when it's hot outside. if you're just going to wear them out for the evening, then that's a different story.
2. When or are you going to go on HRT. You may want to think about that, since in my experience my breast growth made it very uncomfortable to wear forms on my chest. This might not be true for everyone, but it that was my experience. Although you instantly won't have breasts, they will come with HRT if you are planning on going that route.
3. Cost. Does cost out weight the benefits? If you are planning to get HRT, you need to have the cash for that. Also cash for laser/electrolsis, and surgery down the road if that's the path you want to choose.
Personally, I found the forms to be a waste of money for me (key words, "for me"). But then again, I went full time quickly afterwards and I didn't enjoy wearing the forms after that. They were nice at first to get a feel and go out with them to clubs, but the newness wore off fast as they got annoying and uncomfortable to wear.
I know some people who have forms and love to wear them.
It really just comes down to personal choice if or if you don't wear them.