Horse Physiology - determining stride and suspension system of a horse?

I will be in the market for a 13-14 hand horse (within the next 5 years) due to age related issues. My doctor says to keep on riding as it does wonders for my health. I am a trail rider, and now have a lovely well gaited Paso Fino (14.3 hands) that will be my pet forever. I just purchased a lovely Morab with a natrually extended smooth gait (15.4 hands). I wanted a Morab that was shorter but could not find one and will love this Morab and use until I move onto a new horse, perhaps keep 3. My next horse will be 13 - no more than 14 hands, with a lovely smooth floating on air walk, trot and collected canter. Finding a smaller horse that has the natural gait, as well as nice kind temperment, not been used for barrel racing or jumping, very sound, easy keeper, will be quite a challenge. This search will most likely take me all over the country, and will be a rather long process. Horse Physiology: Is there a way (measurement or ratio) in a non gaited horse that determines the horses natural extended gait, smoothness, etc. I have time, am patient, but not willing to fly all over the world to ride potential prospects.

I find that mounting a smaller horse is much easier (I ride trail), as I have a right knee replacement (peg leg) that is not flexible and it is difficult for me even though both horses are trained to wait upon command. I find a rock to stand on, but if I need to come off in the open field, getting back on is rather difficult, especially as the horse wants to much grass and I ride mostly solo (no one else in my area rides trail). I will keep my gaited horse but do want a smaller horse with smooth floating gait. Any sugggestions? Is there a ratio or measurements that will help me? Also posted in pet section incorrectly. Thank You.