This is one of the questions where the ultimate answer is 'it's up to you'.

Some very lovely people only do it with, and some very lovely people only do it without, and some very lovely people do it both ways, depending on demand. But that doesn't matter, see the first sentence

If you do it without... from what you say, you will enjoy it more, but you may catch something, so you will need to include oral swabs in your routine checkups. Some clients will only want oral without.

If you do it with... from what you say, you will enjoy it less, but the chances of catching something are greatly reduced. Some clients will only see you if they think you only do it with.

I doubt size has anything to do with it either way.

See first sentence