Have you really costed out your expenses. As well as the main bills of energy, water, tv license you need to add fuel and tax/insirance (if you have a car), car maintenance, haircuts, money for presents/gifts, little everyday spends like the odd cafe or restaurant meal, subscriptions, any pet expenses, travel if you want to go further afield or take a holiday. I think it’s do-able as a couple but tight. You’d have to live frugally as a single person.
Personally, I would hate to have to watch every penny as I like to go to the theatre, cinema, go on holiday but if budgeting is something you’re used to then you just continue as you were.
If you live in or near a city, there are usually lots of low cost or free things for seniors you can do and social groups (although there is sometimes a cost for these).
I would also s ope out a cheaper area that I’d be happy to downsize too to free up some ‘living’ money. I might be wrong but it doesn’t sound like you’ve had a lot of fun times? Life is for living, especially in the Autumn years.