I used this with clients for a while. The temperature readings weren't as accurate as my supervisors 15 year old ThoughtTechnology monitor but was close enough and seemed to accurately detect changes.

Amazon has quite a bit of these things individually, if you look them up. Example1 and Example 2

I did biofeedback training with ThoughtTechnology's equipment and software but if you google "biofeedback equipment" you should have a pretty good idea of who is near you or can equip you.