Heat Pumps and Electric Heating - way to convert to wide swing 1st stage thermostat

i have a 19 yr old ruud murcury switch stat.
the murcury rolls to one end of the glass tube for on, then a "spring" moves as the temp chnges, the mercury rolls to the other end for OFF.
the spread is only ~1*; it CAN'T be changed.
So if i eliminate the ON duty(add a replacement toggle switch for ON) the mercury has only 1 job; OFF. So it can have any spread i want. If on heat, i like 77F, i can toggle it on at 63, and it goes off at 77 every time.(extreme example not normal!)
For ac a relay will be required i think.(or visa-versa)
anyone like this idea?
it, still has the 1 degree fault, however. once the house warms up it still cyles 1*, so i have a long way to go for the real thing LOL

There are many ways to make a thermostat with as wide a differential as anyone might want.

The easiest way (but user UNfriendly) would be to use two cheap thermostats along with a double-pole relay wired for latching operation. One thermostat (the lower set point) would cause the relay to close and hold in through the "seal-in" contacts and the other thermostat (the upper set point) would break the "seal-in" circuit.

If money were no object I would use something like a Moore Industries SPA alarm module with an RTD temperature input.

Lots of other options if you want to check out the industrial controls field however you won't find anything as inexpensive as a residential thermostat.

thanks for your reply furd!
i have a box of relays,......

but, i think i'll try dampening the response time by closing the air source with some masking tape. it just needs 5 more min before it reacts.

the newer thermistor type should be easy to modify. the thermistor gives a resistance dependant on temp. A Dual Op Amp likely compares the hi-lo range and uses a fixed resistor to end the cycle (set by the maker to what they think people will like). a tech could change the fixed resistor to a variable(costs $1) and give any 1st stage cycle range needed. i'd like to see a schematic of course, but i have a book that shows the workings of the IC if they have a number on it.

turns out the new stat can set the swing 1 2 3 4 5 6 degrees
tried 2, shut off in 3 min.
at 3 it ran 10 minutes.
cool!