I have a Mrs and I've got the same fear as you so I did a ton of research before starting up the hobby. Your primary risk is from gonorrhea. The chance of getting any of the other STDs from BBBJ is almost zero. (Try www.medhelp.org if you want to verify this for yourself.) I believe it takes 10 days or so for G to show up on a test so all you need to do is make sure you get tested before resuming sex with the wife. G is quite curable, though I have read about a drug resistant strain coming to the forefront. My wife and I have sex about 4 times a year so this is easy for me to manage and, quite frankly, if your wife is giving it to you regularly, you shouldn't be hobbying to begin with. Finally, your chances of even getting G in the hobby is minimal since providers get tested so often. That being said, ALWAYS get a test before resuming sex with the wife or you will have some serious explaining to do it you do manage to pass something on to her, however unlikely that may be.
BTW, if you are married, STDs are only one of the things you need to worry about. Get a hobby phone, keep your computer clean, be discrete, and read the boards like crazy. It took me 6 months of research and planning before I felt firewalled enough to see my first provider.