Get a Merc C Class diesel, and automatic naturally. 5k still gets you a decent one and it will drive lots nicer than most cars on the road.
I did this (Merc C Class estate petrol with all the added extras and sports package).
What you don’t mention though, is that every time you so much as fart in the car a random warning light comes on telling you to take it to a Mercedes garage, then the Mercedes people have a quick look at it and tell you to bend over while they bum you, stealing your wallet at the same time.
I’ve been quite lucky so far, but unless you are very handy with DIY mechanics (which I think the OP said he was not) then pretty much anything going wrong with an older Merc costs a lot to fix (even through an independent).
I love mine, but there’s always that niggle at the back of my mind that if something goes wrong it’s going to cost big bucks. Buying a Merc isn’t that expensive, owning one is though.