Mine is from Jason INternational. It's 19-inches high. Note that if the tub does not come with a built-in tiling flange, most of the manufacturers have add-on tiling flanges for their drop in tubs. Many also have optional skirts if they aren't built-in.
Keep in mind that when you add the slanted back, the actual tub opening you sit in ends up being shorter. If at all possible, you might want to consider redoing that space to allow a longer tub. From a maintenance viewpoint, an air tub is much easier to maintain than a jetted whirlpool and you can use oils, scents, bubbles, etc that are verboten from most whirlpools. I ended up with a 6' air tub, and would really have loved a 7' one!