(This is a guide that I can in the future link to because I spend far too much time writing this over and over again.)
Reusing your old Rift or a second hand Rift for Full Body Tracking (FBT) is a good and cheap solution for FBT. With three touch controllers (legs and hip) it is akin to Vive trackers in tracking quality, while being superior with its AA batteries, which allows you theoretically infinite battery life. (PLEASE USE RECHARGEABLE AA BATTERIES)