Hi Bumps,
Thought this would have had some responses by now, but here goes. I've not been private owner myself, but have been in a syndicate (and involved in the running) and helped source/manage a few aircraft for people I've taught to fly.
By saying you want instrument certification, you are putting yourself into a CofA, EASA regulated (probably), factory-built aircraft. Are you sure you need this? What types of flights do you think you will be doing and where? Do you have, or are you planning to get an IR or IMCr? If you can stay VFR, then that opens the door to LAA permit types, which are much cheaper to run. But if you want 4 decent sized adults and fuel, with IMC capability then they're not for you.
How about one of the fixed-gear PA-32s, they have a degree of commonality with the Archers you're used to. Fixed U/C rather than retractable to keep insurance and maintenance costs under control. Being a six-seater, you can actually put 4 people in it, with reasonable fuel and some baggage.
Cessna 182s are quite nice, bigger, faster and more payload than a 172, personally I like the Commander 114B or 115.
There's also TB20s, but there's a better person than me to tell you about those, and the lowdown on ownership.
The N-reg situation is looking like it's going to become tricky once EASA take over, have a search for previous threads on that particular subject.
If you get something on a G-reg, be very careful where you get the maintenance done, since EASA part M came in, it's got stupidly and pointlessly expensive and unscrupulous CAMOs/MOs can have you over a bit of a barrel if you're not careful. I'm sure they're not all just hiding behind the reg's and ripping customers off, but some are
