Interesting concept, good start, but the collection of designs needs to be far more fleshed out. In the gaming chair, you make some bad assumptions (why do people shrink between middle age and 60?) It would be better to use height. If the whole point is customization, the people who are going to want your product are the extremes, like the very tall and the very short. You should ask not just for height, but measurements like (heel -> back of thigh), (back of calf–> back of the gluteals when seated). For the very fat, you need to worry about compression strength, and torques in the pitch & roll planes. Yaw is less of an issue, but if one is designing swiveling furniture like gaming chairs, you need to have the bearing and pistons be able to handle the increase in normal force. I am sure you can google some measurements like the proportional weight of the different pieces of the body (thigh, arms, etc…) at different BMIs. This kind of data lends itself very well to computation. I’m not sure most people can 3-d print metals, but maybe you can set up a C&C machine. Depending on where you live, production costs may be low enough that this can be a profitable venture. I can see this being a great way to sell flat-pack Ikea-style furniture that has been designed by machine for the size and weight requirements of the individual.
I date a very short woman, and have an entrepeneurial mind, hence why this issues are near to my heart.