This is clearly worrying you a lot Claire, and I'm sure you know what are safe temperatures for guinea pigs.
Pop a thermometer in their room, extra hay, fleecy hides, snuggle safes, a blanket over the cage at night- but ultimately, I think you need to sit down with your husband and have a conversation- relationships always have room for negotiation, it bothers me and I'm sure many other women here when you say "husband says" and there are rules you have to follow in your own home.
We are all feeling the squeeze of spiralling energy costs and runaway inflation, but if you and your pets are home all day you may get cold and need to use the heating. Cold nights, of course you need the heating on a bit, it is always false economy to let your house get too cold anyway, as it costs more to heat up from cold than from ambient!
As you are a person with mental health struggles which also impact your physical health, this isn't a helpful approach, someone setting rules which make you worry constantly about your pets.
Your pets are part of your family, and knowing they are happy and healthy is an important part of your self care and managing your anxiety, and I think your husband should acknowledge this?
Probably your piggies are fine, indoor temps rarely fall into the danger zone, especially if your piggies have adapted to autumn temperatures slowly with no big sudden changes.
But you should not have to compromise on basic needs like a moderately warm home on cold days, just because your husband says so. Sit down together and get the accounts out, see exactly what the heating is costing per hour vs what non-essential items are costing, and take an active role in the budgeting.
I watch my smart meter avidly and I know it costs me 26p for 15 mins of central heating- but, boiling the kettle costs 10p every time! 27p for 20 minutes of electric oven vs 30-40p energy for a slow cooker meal.
Take control of putting actual prices on half an hour of heating, vs other expenditure, and I am sure you can find a compromise that allows you to worry less and the piggies to stay warm x