I don't agree that bulldogs take longer than any other breed to potty train. They are very smart and want to please us. TAnk was quick to learn how to make it, after 5 months old ( we have him from 8 weeks old) we never had poop accidents, just 3 random peeIng accidents, something about marking, probably, he never did it lately anymore. 3 times he just looked in my eyes and weed into his own bed :D but not anymore.
But I must say that I was at home with him. I don't know what is your situation with work and time at home.
My tactics was (as we stayed in 21 floor apartment in China): first thing in the morning I grab him and carry him outside, where he does his business. Lots of appraisal and treats. After breakfast grab him again, literally not letting him walk from bowl, and carry him downstairs. Also, we had at home a plastic toilet with pee pads, where I put him every hour or so, asking him to make a wee and giving him treats and kudos. He never pooped there, though, but very soon he got the idea and came to n the toilet himself and made a pee.
The idea is to be very persistent, as puppies cannot keep in mind yet in this age when bladder or butt is full, that it's necessary to carry it outside. When they really need to go, they already NEED to go. It is often too late for them to think where to pee or poop. It just comes out. So, your job is to prevent accidents by often reminding them about toilet. May be a plastic toilet at home near door could be a helpful thing for now. But from my experience (I had 6 dogs in my life, 2 pure bred and 4 rescued), healthy puppy learns toilet skills in 2-3 months. Of course, it also depends on how much time you can afford to dedicate to training.