Welcome. And I see you received your sexual education in the United States. First off let's start with that in general escorts are better about using protection than the general population. It's true that only some escorts require protection for blowjobs, but the general population almost never uses protection for oral sex. Those diseases you've heard about that you can get even while using a condom are that way because they are incredibly contagious. So contagious that if you are an adult you are almost certainly carrying them already. Most adults carry herpes and HPV with no symptoms. Even nuns get herpes and HPV and sure that's because some of them are having sex but not all of them.
This should help you out:
https://youtu.be/aU4VcOQzQm0
The morality police have been using those diseases to scare people about sex.
As for the others like colds and flus the majority of people you meet are not sick, even people who have lots of contact with lots of people. Also like colds and flus just because you've been exposed to someone who is sick does not mean you will get sick. So in your favor you've got that the majority of people are healthy and even if they're not the odds of you getting sick aren't all that high. Even if you do get sick the odds are your immune system will deal with it. Still you should use a condom for full service. Getting HIV would still suck, and if you don't have good health insurance might even kill you, but take heart that that is very very unlikely to happen either way. Using IV drugs and sharing needles is way more risky than sex, especially for men.