Couple things....
27.5” and 29” wheels don’t make a bike fit “taller”. That is a very common misconception. BB height is independent of wheel size.
Something sounds screwy, here. My inseam in only 1” longer than yours (I too am freakishly proportioned) and even frames with 19” seat tubes (large) and top tubes I could not stand over leave me with almost 6” of exposed seatpost. I can’t see how it is possible you can’t easily get on the bike with the saddle all the way down.
Something is just not adding up, here.
how long is the seat tube on a Medium? 17”? Even with legs as short as yours, you should have at least 5” of seatpost showing at full riding hieght.
Something is missing from this story.