annepl - have you checked your area to see how many nightime breakins into domestic homes actually take place. Think you will find it very very rare.
Why are you so scared of this happening. Do you have loads and loads of expensive jewellery and art things that professional thieves may be after? But even those would choose a time when nobody is likely to be in.!!
I would NEVER permit any sort of lock, key or bolt on any indoor door when my children were at home, and the key to the backdoor was always in it and the front door just had yale lock. In the even of a fire or similar problem, the everyone would be able to get out easily,
I have lived by myself for decades, most of the time in East London, Still have he same rules - no bolts, keys in rear exit doors, etc. Also a key safe for my front door, so that number could be given out to emergency services to get to me.
Upto last year, have lived all my life in East London area, never had any problems with break-ins.