The vast majority of weeping/cascading Japanese maples tend to be of smaller or dwarfer stature than do upright forms. But that doesn't mean they can't achieve a decent size over time. What you want to look for is graft location and training. Both of these criteria will have significant bearing on how tall the tree will ultimately grow. Look for varieties that have low grafts and have not been excessively trained to grow vertically -- these will develop that weeping, cascading form at an early age and never attain significant height.

Some varieties for you to look for/consider: 'Garnet', 'Red Dragon', 'Tamukiyama', 'Inaba Shidare', 'Red Select', 'Crimson Queen'. Any of these can remain well within your heigh requirements with low graft and proper training but they can also get quite wide with time.

FWIW, you never want to prune a JM to maintain a specific height - you will ruin the form of the tree.

Thank you for this detailed reply gardengal. I now have a starting point with regards to possible specific JMs.