I don't know about a wand-only extractor, but Bissell has a unit that is small, portable, and self-heating. You can find it at Lowe's, many others, or on-line.
I personally use the non-self-heating model, as it was more affordable. Considering that the kitchen sink is only a few steps from the garage, it is not much of a loss for me.
I only use the extractor for removing the detergent, after I've worked it into the carpet/upholstry, and allowed it to set for a while. When used in this way, I don't know that there will be a significant difference in effectiveness with the additional temperature a self-heated unit will have.
The results that I get with the non-heated unit are very, very good.
Good luck with your search.