There are many different kinds of repellants and some work better than others for some people vs. other people. There is no 'one size fits all'.

Avon Skin So Soft has long been known by N. American backpackers as a bug repellant. Avon finally figured out why they were selling so much of it and came out with Avon Bug Guard which sells for more than the original Skin So Soft. LOL

https://www.avon.com/category/bath-b...ect-repellents

You can still just buy the original Skin So Soft for less money.

You can try it but all repellants work better on some people than on others as I said, there is no one size fits all.

I guess trying some repellants is your cheapest way to try and solve your problem but you may have to try several before you find one that works well for you and in the meantime you will continue to get bitten. You could make up some wooden frames with screening if you or someone you know was handy with a hammer and nails and use them in your windows temporarily. You could buy an air conditioner and close your windows, that would be the best long term solution although the most expensive obviously.

I guess the question I might ask myself is do I believe in Global Warming or not and do I believe the scientists who are telling us we better get used to these weather changes as they are going to become the 'new normal'. If you do believe that, then adding air conditioning as a long term investment would be the way to go even though it has not been the norm in the UK.