Make sure its durable enough to last you for years and that it is adjustable, mine can be sewn smaller (the seams are on the outside as not to irritate the skin). The rep who set me up with my pump said he'd never seen anything like it for the price and durability. I have 2 full length in black, 2 full length in beige, 2 full length in off white, 2 below the knee length in beige. I also found compression stockings on drugstore.com for extending the length on the below the knee ones. I had tried spanx and they were not durable. Jobst brand was way too expensive.
Drugstore.com sells pantyhose style and knee high style.
Amerimark.com sells the knee high style a *****eaper than drugstore.com