Hi NewWings
Keep logging with the police any evidence that you have, that someone has been in your property, also you could speak to your neighbours in case they have seen or heard anything strange when you have not been there.
It sounds like you have put in all the obvious security measures, you could get extra window locks if you think someone might be getting in through a window. Your local domestic abuse support service would normally offer some support with home safety if you haven’t contacted them already.
Take Care and keep posting
Lisa