If you can't find a doggie style heating pad, might look at heating pads for farrowing crates. links below. If they can survive an old sow with a litter of piglets, I don't think your Dachie is going to hurt one. Bottom link is small one specifically for piglets. $87 USD.
https://www.google.com/search?as_q=...e=images&as_filetype=&as_rights=http://www.qcsupply.com/250200-kane...3Pigd35c2QW9PGTaMN2gXscBdAxVqhoC8PLw_wcB
