Hi diynaturalbedding,
While I don’t have personal experience with any of these … like the other comments here I would probably use a heated mattress pad that is designed to withstand pressure rather than an electric blanket if I was sleeping on it rather than under it. Good Housekeeping has a few reviews of some of them here and Apartment Therapy reviews some of them here and the so called “electricblanketinstitute” reviews some of them here (but they all lead to a commercial site that sells them). Sleep Like The Dead also has some amalgamated reviews of some here. Sunbeam also makes a version that has 6 heating zones here.
Many of the retailers I’ve talked with think highly of the ChiliPad technology that dn mentioned which uses heated water instead of electric wires and can both cool and heat. They also have a mattress here that incorporates the technology into the mattress itself and there is one manufacturer I know that is using their technology in their mattress as well here and he has told me that you can feel the tubes even less when they are inside the mattress than with the separate mattress pad.
There is also a similar product here that is based on water.
Sleep Number also has a version which uses heated air (and this thread has a few comments as well) and the YuMe mattress also has a version here that uses air as well.
The Craftmatic adjustable bed here also has a heating option.
Based on the conversations I’ve had with others (since I have little direct experience) and if regular more “passive” temperature regulating methods (such as wool) weren’t enough … I would probably lean towards the Chili Technology if I was looking at an “active” heating system in spite of its relatively high cost.
Hopefully any other members that have experience with any of these or have any other ideas that relate to the original post will add their comments here as well.
Phoenix