There are differing build techniques with stone depending on the type
of stone - compare for instance the small slab stones on the
Northumberland moors with the great chunks of granite in Aberdeen.

In my own cottage - sand stone and whin - the walls are approaching 3
ft thick and consist of outer and inner skins of large stones with lime
mortar, and all the rubbish - and that is what it was called - goes
into the middle without any mortar. It's a real pain when you are
making a hole right through for pipes,etc as the small stones just keep
on falling down.

Now to insulation - the original stone floors were replaced in the 20's
with fully vented wooden floors and the walls were lath and plastered.
Unfortunately they hadn't heard of insulation then and all the
underfloor ventilation went up to the roof space behind the L & P;
result freezing cold rooms permanently. So off with the L & P -
restrap, rockwool, membrane, plasterboard; result warm house. That's
the way to go but it is possible that may not work for you.

Rob