The only thing I can add is from my own personal experience, which is coming straight from BA to PhD. When I realized this was the path I wanted to take I originally expected to apply to MA programs, likely at the same school I was already attending. I had no idea how any of this stuff worked. But, in talking with my advisers, I was told it would behoove me to try and get into some summer research programs to show that I could do the work. I ended up going to two summer research programs where I produced two different 20 page papers and also took a graduate seminar where I produced another 20 page paper. I think, in my case, the ability to research went a long way to show that I was capable of doing work at a higher level because my checkered undergrad history certainly didn't do that at all. I do think that to go from BA to PhD you'll have to do a lot of work outside of the BA to indicate your capabilities. Independent studies, honors thesis, summer research, etc.