Bump Proof Locks
Bump proof locks are available starting in price from about $30.00.
If you buy a keyless entry lock that operates on batteries it will have a key override in case the batteries fail. Make sure the key override cylinder is bump proof.
Mechanical push button locks don’t need batteries and some have no key override so you don’t need to carry a key or worry about being bumped.
You can also change the combination on these locks yourself.
If you have a deadbolt and lockset, you may be able to just replace the deadbolt and still have the same key for both locks.
Additional entrances could be secured from inside by preventing the thumb turn from moving or adding an additional locking device.