I'm not a huge supporter of the ankle carry method. It's slow & awkward to draw from in a critical incident. The weight & size may also take some adjustment. It could also feel wierd & unbalanced if you walk-run.
If I were to use a ankle holster for a BUG(back-up) or 2nd gun, I'd wear the rig on my right ankle(inside). I'm left handed & like the way a inside ankle holster is concealed by the leg. A few top brands for ankle carry include Bianchi, Alessi, DeSantis, Galco, and Ken Null.
Many gun owners & LE officers like the Bianchi Ranger style and the DeSantis.
Sheepskin formats are popular because they breathe(good for hot weather) and are comfortable.
As for revolver vs semi auto, I'd lean towards a 5/6 shot snub. Grit, dirt & lint can cause a pistol to jam quickly.
Clyde