Don't know where you're located Simon. However, if there's a crime prevention officer based at your local police station, they'll come out, take a look around your property and make some recommendations. If there is such a thing as a crime prevention officer these days.
Same as cars, opportunistic thieves will check doors and if left open will lift anything that's easily sold on, like jewellery, electronics etc Cash, obviously.
So, yeh, locking your doors would be a good first step
I don't wish to worry you. However, statistically, when you're the victim of a domestic crime, you're much more likely to be a victim again very soon. Thieves who steal, know that house insurance will replace items pretty quickly and for that reason, amongst many, may revisit a property to try to steal the replacement items.
If I was this little so n so, I would definitely come back, because in time, you may go back to your old behaviour of being lax with your security.
Safes are a whole subject of themselves and if you PM me, I can give you basic advice. You'd be better off talking to a specialist, if you feel that you have valuables that warrant the expense.
Cheap deterrents include. Motion activated lights mounted high on external walls. Overlapping and covering every external entry point, at least. Real or fake CCTV cameras, mounted high. If fake, ensure they're not of the common fake variety and ensure there's an attached power lead and light showing the camera is powered.
Join your local neighbourhood watch scheme. If one property suffers a crime, I believe the rest are notified quickly?
Or local Facebook neighbourhood group.
Powerful lights, motion sensitive, are a powerful deterrent. As are cameras. Most thieves will be habitual and if they know police might obtain an identifying image, they will be easily found and arrested.
You've had a near miss. Use the opportunity as a wake-up and take some basic, inexpensive measures and its unlikely you'll have a forced break-in in future