If you're referring to "Swim Spas" then I am sure there are many people here that can help. Swim Spas are usually free-standing resistance pools that sometimes have a separate body of water on one end that is a hot tub.
I carry Catalina Spas, the first swim spa manufacturer. They're also one of the least known swim spa makers on the market as they don't advertise themselves. More well-known brands are Master Spas and Endless Pools (the latter of which doesn't have a brick and mortar store but rather is a direct-to-consumer business.
Almost all swim spas are 90" wide, as that is what Catalina ordered their shells in 30+ years ago when they developed their first swim spas. Most units run from 12' to 18' in increments of 2' (depending if you're measuring outside, inside, etc. you may have variations). There are units smaller and larger but they are few and far in between.
The 3 most common forms of resistance are circular jets, propellers and river water jets. Ask 10 people what the best resistance is and you'll get 10 different answers, depending on who is selling what. Best thing for you to do is to wet test. Its no different than a hot tub: Comfort and wet test are the determining factors. The rest is just details.
Do your homework: Find out what brands are in your area, who carries them, how long they've been carried, how long the brand has manufactured swim spas, etc. The last part is important as swim spas are new to the industry and many manufacturers are on their first edition. And the first edition of anything is never going to be the best edition as the bugs haven't been worked out.
Once you've found out what is available to you and have visited the showroom you should come back to the forum and tell us what you're zeroing in on. Again, I am sure there are others who can speak specifically to the individual brands you are considering.
Expect to start in the low to mid-$10k's and go up from there. You're going to need a base for it, a crane to deliver it, and electric ran to it.
I hope this helps. Good luck moving forward.