Most police forces have something called the bobby van. If you receive certain benefits or have been a victim of crime its free, they fit all the necessary locks but they can certainly advise you. Get in contact with you local station. On my inner door I have a yale lok, another lock that you can open the door a few inches without having to unlock it, and huge bolts at the top and bottom, so its secure in 4 places, so its basicly reinforced even if someone is trying to bash it down it would take an age to get in.
I had a smiliar thing happen a few years back, I noticed someone snooping in my back garden, so I phoned the police, much palaptations were being had. They then asked if I could still see him, he had his arm through the kitchen window (one of those little flap windows, trying to open the big one. So I grabbed the handle and started banging his arm with the window, he was screaming I was screaming, the police were there in 2 minutes lol