This is a VERY simple mod IF you can get the correct part. The little locking lever is virtually a push-in part, with just a small sprung pin to retain it. The catch (no pun intended) is that the lever is handed, one for the left hand door, one for the right. You MUST get the right lever, or it will turn backwards and foul the B-post.
To order the part try the Birmingham centre, Mike has got them for me before, just specify that you want the lever for the RIGHT HAND door. If you think about it, on a left hand drive car, this is the passenger door!! Even if they are not normally fitted in the UK, they are made for the export market. The levers are not expensive.
Once you've got the little lever, simply remove the rubber grommet from the door. Also remove the trim panel so that you can see what you're doing (unscrew window winder, door lock lever, and door pull, and then gently prize off the panel). You can now see a little hole in the lock assembly. Push the lever through the hole in the door and into the one in the lock. Lubricate. Refit panel and handles. Job done.
And by the way, yes you can still open the door from the inside when it's locked from the outside, the lock operates only on the outer handle.
One word of warning: If you leave the keys in the ignition and then catch the lever on the door as you get out, you can lock yourself out
Good luck, stay safe, that's not being a wimp, it's being sensible.