For oral without you can catch or transmit
Chlamydia
Gonorrhoea
Herpes
Hep B
HPV
Syphillis
Chances of a male catching HIV from a female, from normal sex, 2500:1
As I've posted elsewhere, Hep B you can't catch from oral, unless the WG has a very bloody mouth. It's not carried in saliva. Just blood/semen/vaginal fluids.
Herpes, you can both catch and give through oral, but HSV1 is 70% by age 40 in the UK population, with most contracting it in childhood (oral herpes), can't catch that a second time. HSV2 has only about a 10% rate in the UK, and the burden does fall more on one subsect than others.
HPV, there is no test for men. So no proof with respect to that.
The rest, studies have only show giving it, I do realise some have noted recieving it, but risk is very low.
Bareback is a lot greater, and offerings are all down to demand. The increase in PrEP I could see upping it in areas, and much like the gay community, I could see it increasing other STDS (syphilis has jumped up in cases a lot since PrEP can in). While the offering may be there, be smart and stick to a rubber for penetration.
If you don't like someone who offers bb, don't book them. Money effects trends a lot.