If it's a wooden door, it's usual to have a British standard 5-lever deadlock, and a British Standard Nightlatch.
A good-quality deadlock at reasonable price is the Union with the red case examples
Such deadlocks need a key to lock and unlock, so if you are anxious about being locked in you don't have to lock it at night, but should do when the house is left unattended. A BS deadlock is particularly strong and secure.
A nightlatch works like the old "yale" type latch, and will automatically catch when the door is closed, and you can open it from outside with a key, or the knob from inside. however the BS versions are much stronger, and have a large, armoured keyhole guard on the outside, to resist attack, and can be deadlocked with a key if you wish. In your case you might not deadlock it at night, but should do when the house in unattended.
You will notice that they are bigger and more expensive than "traditional" low-security nightlatches, which are very weak and insecure.
examples
The Yale brand are more expensive than most, IMO because you are paying for the name.
When you have these two on the door, fit one a third up from the bottom, and one a third down from the top. If there are children in the house, the nightlatch is usually fitted as the higher one, where it is more difficult for small children to reach.
Don't leave a key in either type of lock, even on the inside, because there are simple techniques for a burglar to manipulate them from outside, especially if you have a letterbox or glass panel in the door.
If you want to keep a key handy, screw a cuphook into the door frame, on the inside, at the hinge side, high up, where it will be out of sight and out of reach of anyone outside.