As a big man, a backplate with a wing is guaranteed to fit as you can make the harness as large as you want. Conventional or Standard BC’s, even XXL’s may not have enough flexibility in adjustments to guarantee and comfortable, secure fit and most will not accommodate sufficient weight holding capability for a large man in a 7mm full suit.
However, regardless of the repeated chants you will no doubt get in this (and virtually every other one) thread, BP/W is not the end-all-be-all for everyone. I use a Apeks WTX harness system. It works well for me and I would not trade it for a simple BP. If I decided to use doubles, I can add a plate to the system. The system is very secure, flexible and comfortable.