Hi Teddy,
Getting the right bra can be challenging at best. I have found that band and cup size vary depending brand. I have my favorite two brands and when I deviate from them I can't just grab one off the rack, I find it will either be too big with my breasts swimming around in the cups or too small with me spilling out everywhere and a band that's a bit too tight. So I go try them on.

If you have your favorite brand and it fits well then go with it, if you want to try something else definitely use the fitting room or even get a bra fitting from the expert running the shop or bra department. Trust me they don't care if you're male or female they want the sale and a return customer, because they know a good fitting bra is difficult to find.