My advice on being more secure would be to go and buy a more secure safe. They make some really nasty devices in the safes made today like glass plates (that breaks if you try to break in and set off some other locks) and other things to make it harder to get into them. It all comes down to what are you protecting and start there. What is it worth? Are you protecting against fire? Older fire safes were only good for maybe 20 years before there fire protection dried up. The new fire protection doesn’t dry up. So there are some things to think about and go look at different safes to see what is out there.
I wouldn’t bother with trying to add anything to that safe if I was you.