Welcome to the Forum and thanks for your questions, I'll be pleased to provide some information.

Condoms remain the single most effective means for reducing the risk for STD acquisition when one is having sex with a potentially infected partner.  Condoms have been extensively studied in terms of their ability to protect from HIV, gonorrhea, chlamydia, trichomonas and herpes. With the exception of herpes, for each of these infections, condoms are close to 100% effective when used correctly.  For herpes, estimates are that condoms reduce the risk for infection by about 60%, presumably because they do not cover the entire penis all of the time (this is pretty good when one also remembers that the risk for getting herpes if one has sex with an infected person who does not have active lesions present ins less than 1 infection per 1000 sex acts).   Even with all of these studies it is important to understand that the estimates that these studies provide for condom effectiveness are probably overly conservative since there is no foolproof way to determine that people who say that they used condoms actually did use them and used them correctly.  I would also add that available data suggests that when condoms fail, they break wide open and that condoms do not tend to "leak".  Finally I would add that all available data suggests that condoms still work if they happen to slide off as partners separate after sex, leaving the condom behind. 

Condoms clearly reduce the risk for syphilis and HPV but how much is difficult to estimate.  Syphilis is a rare disease and hard to measure, and most people already have HPV making condom effectiveness hard to measure as well.

Finally, it is difficult to precisely quantify the risk for STI from receipt of unprotected oral sex.  Most people do not have oral infections and when they do, infection is not very efficient from a biological point of view. the most common infections resulting from receipt of oral sex are non-chlamydial NGU and gonorrhea.  Both these problems usually cause symptoms and are uncommon.

I hope this information is helpful.  Congratulations on your approach to safe sex.  it will do a good job of keeping you safe.  EWH