Scientifically speaking, how can I avoid STD's when using prostitutes?

So far I have only received oral because they hopefully use mouth wash, and its rare to get HIV from blood leaving a wound, and I'd need a wound on my penis too...which is also flowing outward.

I've been thinking about bacteria from the skin to skin, and I would like to try penetration too.

I am thinking that using an anti bacterial spray/gel, all over my crotch and penis just before the sex would work? almost creating a thin layer of anti bacterial film over my skin that will contact the woman during penetration.

Any other solutions? are there powders that can make the skin anti bacterial temporarily?

inb4 testing because I can't afford that, and inb4 non prostitutes, I can't afford these either.

Is there also a way to get my crotch region tested for STD's? the last clinic I went to just looked for aids in my blood.