I had problems too but now I wear Equitector riding boots. They made a custom pair for me and they were quite reasonably priced.Foot size I was just outside the range but it did not seem to matter. Just love them.
My calf is 18 inches and I wear Equitector riding boots. They fit my chunky calves perfectly. I bought them on line, they have a brilliant website, where you can put all your size details in and it works it all out for you. They are so comfy these boots
My butt is on the bigger side... and I had never bought breeches, so I was expecting them to all run small (come on, we've all seen the models in the ads - the breeches aren't even flattering on THEM!). I was pleasantly surprised to squeeze my butt into a size 34 and still have extra room. Then, I went to get another pair one day, and I was so sad that the 34 I tried was more snug than I was comfortable with (I hadn't grown, btw). I decided that I should probably do as much work on the ground as I make my horse do when I'm in the saddle ;) Of course, my favorite brand is the one that so kindly fits me into a 34! Hehe
Boots - I was terrified that the boots my husband bought me for my birthday were just going to be awful to break in/wear. Soooo not the case! Although they are by no means top of the line, I smear them with leather grease in all the "bendy" spots BEFORE wearing them, then smear them again after wearing them and let it soak in for a long time, then clean them. They are wonderful! Granted, I wouldn't want to run a race in them or anything...
I have found the Dublin boots to have the best sizes for fuller calves and shorter legs. And they are a great price around $150.
As far as the low rise breeches. I would avoid them if you are heavy in the bottom area. They are just not flattering for anyone larger then a stick. Also, from a judge's point of view they give a false picture of your postion. If you watch a person with low rise breeches on ride they look like their back is rounded. This false picture could make you lose points with a judge.
The Kerrits Flow Rise breeches are high enough in the back that you don't have them going down too low. They are pretty tight but I personally think they run a bit large. I have several pairs in size small and they are a tad bit too large.