Don
At 7mm I'd just replace one.My C63 is on P4S tyres. The previous owner replaced one due to damage so now I have one that needs replacing and another at 7ishmm. Not sure if I should replace both or just the one. If I replace both I'm putting Goodyear Eagle F1's on. 265/35/19 pricing is obscene. I can put 275/35/19s on for much less.
In the event that you did replace both, surely you could retain the tyre as a spare, and then would only need to pay fitting in the future?