It really depends on the money available. Personally if you are staying in the house I would put some solar up - energy is only going to increase in cost going forward and you could easily cover day time useage with solars and if the money stretches maybe a battery for overnight tick over.
Windows I am not sure you get the same savings and return it kind of depends what you have now.
I would consider putting some within a pension fund as longer term you sound as if there will be a period of low or no income where pension wont be a priority but this could leave you in dire straights once retired so a boost now could really pay off longer term.
In terms of the house inside - what kind of heating do you have? This could make a difference - we have a log burner and LPG boiler but you could invest in a low costing system that could reduce energy costs even further e.g. if you have access to wood and space to dry it then this could potentially mean a log burner for the living room would reduce central heating use significantly.
Think about how and what you cook, Do you need a stove or is the slowcooker, a decent air fryer and microwave "going to do you". Consider what you eat and how changing that could help you reduce food costs - e.g. Would setting yourself up with a greenhouse and some beds be a good move (are you green fingered) things like salad are expensive and you can grow some more expensive veg that can be used to stretch your budgets. More use of good fillers like lentils and chickpeas etc in your recipes could help keep costs down - maybe some cooking lessons on this different way of eating would be a good investment if normally that is not your thing. Also reduce use of expensive things like meat and sugar/treats. Consider using click and collect shopping for more basics so you are not tempted to buy off list items (although you miss out on yellow stickers)
I would make sure my white goods were on a good footing e.g. 6 yr old washer I might consider replacing now same for a fridge freezer - maybe increase the freezer side to help with batch cooking of making use of yellow sticker bargains
I would review clothes and shoes for your new way of living - if more walking etc then good walking boots and waterproofs including trousers could help. Or maybe bikes would be a good investment.
Consider some training for a side hustle - so if retiring this could be something you do part time so that there is possibility of some income from somewhere if needed.
I would have an emergency fund for sure.
Cars - if you are keeping, get them looked over, consider new tires and any work now or possibly upgrade to newer models with potentially less maintenance. If have two can you make do with one and upgrade it to newest possible esp if this is retirement as you are unlikely to be able to upgrade again.
Could the money be used to add quality of life e.g. a Caravan site or similar that you rent out as well as use for breaks yourself. Do consider how far away it is though and what it would cost to get to etc.
A friend of mine in a small town over time bought 3 little shops freehold and now rents these out for passive income. They are local so he can keep an eye and they are on repairing lease so shopkeeper maintains etc (very different to residential rental) Just be careful to pick somewhere where they will be rented rather than sit empty.