Hi NiceGeoff,
The first place to start your mattress research is post #1 here (in case you haven’t read it yet) which includes all the basic information, steps and guidelines you will need to make the best possible choices (and exclude the worst ones).
Once you get to step #3 … if you let me know your city or zip I’d be happy to let you know of the better possibilities or options I’m aware of in your area (many of the “best” mattresses in the country are made by smaller independent factories and are only available locally or regionally). Once you have done some local research then you also have some good online choices that may also be worth considering depending on what is available to you locally.
An eastern king size and queen size mattresses are both 80" long and you are 73" long which means they would be 7" longer than you are if you sleep fully extended and not at an angle on the mattress. You can see some size guidelines in post #2 here so you are “on the edge” in terms of whether you would benefit from a mattress that is longer than a queen or eastern king size (a california king size is 84" long but is also narrower than a regular king at 72" instead of 76"). I think most people of your height would be fine with the length of a regular king or queen size mattress but it would depend on where and how you tended to sleep on the mattress and on how close to the end your feet are in your normal sleeping positions. It would also depend on the importance to you of having more width vs more length. Your choice could play a role if you are or plan to sleep with a partner and how much individual space you prefer when you are part of a couple.
Phoenix