I understand that problem, I've bought the wrong size before and the "snug" feeling and security is greatly needed pre-SRS. I choose to wear bikini style as it has enough fabric to cover things as well as pull the back up a little like semi thong back to hold it there. I can wear normal thing or G-String yet as there is not any fabric to hold things snug and secure. But God willing, once I can finally save up to have SRS, that problem will be gone, and I will have the freedom to wear all the things.