Lost key!

[threesecrets]

I have a bedroom door which has a lock and key. This was very handy for privacy.... until the key has been misplaced.
I don't think we are going to find the key.
How can I fix this? I've been googling but can't really understand. Am I right in thinking I can keep the existing handles but need to get a new bit to go in the inside? Pretty much DIY novice so hoping for some advice. I've looked on homebase website and can't work out what to buy. Basically need a new key and the bit it goes into!

Yes you can just buy a lock with 2 new keys and fit your existing handles into it. Just measure your lock on the side of the door so you get one the same size. It will save you having to enlarge the hole in the door or the hole on the door frame that takes the lock.

Ah great. I wonder if I can unscrew the lock bit to check the size or whether I have to take off the whole handle.

Update- husband found the key!