I normally change locks when a tenant leaves and I find it easier and cheaper to buy replacement keyed alike locks than faff about with keys.
Assuming you have Euro cylinders (pretty much standard now days) a web search should be easy to find a new lock set with multiple locks and keys or a single lock with extra keys (expect to pay around £50-60 for a new high quality lock and 5 keys, but cheaper locks are readily available)
But if you buy 2 locks keyed alike and 6 keys you will have the same key for both front and back door, if you go for thumb turn internal you’ll probably never use a key in the back door anyway.
BUT be aware Thumb Turn have a downside, with thumb turn locks, you can’t lock a key holder out, that’s fine if it means Hubby can always get in while your in the bath because your key won’t be left in the lock, baring his key from working, but maybe not so fine if you’ve just kicked hubby out and don’t want him coming back in.
Us landlords fit thumb turns simple so tenants can’t lock us out, but believe me most Landlords wouldn’t have them at home.