^ That's a fair point Rosemary.
We looked at a ground source heat pump, but didn't get one in the end because we weren't prepared to insulate and draft proof the house to the extent needed to make it work well.
If you are though, or if the house is already well insulated, a GSHP or indeed air source could be a really good bet. They're well suited to retired folks since they produce a nice low-level heat all the time, and also run entirely from electricity so there's nothing to either lug about or run low on.