If you could squeeze 4.31 m onto your drive you could get an Approved Used Kia Ceed with a 7 year warranty.

Seat comfort and driving position are such personal issues that it's hard to advise someone else. What's comfortable for me (5'7") may not be so for you at 6'4".

What make is your estate car and are you comfortable in that? In which case try a smaller car of that make. Also you could consider an automatic, as pumping the clutch may be contributing to the pain, at least in the left knee.

If it's any help, I can say that I'm now 72 and have never had a single ache or pain in any of the VW Group cars I've had, nor in a Volvo.

In addition, whether a car has a left foot rest and its size (some are too small to be of any worth) can also make a difference, depending upon how the driver rests their foot.

I've found that the size of the car doesn't always have a bearing on seat or driving comfort. My neighbour's Picanto is much smaller than my Mazda3 but is actually higher. The main issue with smaller cars is often the lack of width, or, with lower spec/older models, a lack of seat and especially steering wheel rake and reach adjustment.

I had back problems with my mid 90s Micra (a car with a decent amount of headroom) because I had the seat one notch too far from the steering wheel. I was lucky that as someone of average height, I could move the seat forward a bit and not make too much of a compromise otherwise.

Perhaps if the OP can find a car with more seat and steering wheel adjustment, this may help. In addition, some cars have their pedals more offset than others.

When I was looking for a replacement for my current car, I tested or at least sat in (to test the driving position) a good few cars, and some (e.g. the Nissan Pulsar), whilst very spacious, had offset pedals (which could easily cause back and leg problems even if the seat/steering wheel adjustment was good), others like the Volvo V40 (current shape) had no foot rest.

Some cars also aren't so good as regards the ergonomics of the centre console area, meaning you sometimes have to reach quite a bit to get to the controls - made worse if those other issues I mentioned are in play.

Hi..I am similar size to you, we use a Kia soul as our runaround which meets all our needs, its what I would call a small big car, we got the automatic which is a dream to drive, its also has a slightly sat up driving position which adds to the ease of getting in and out,

I can't say anything on the ability of cars to accommodate someone of the OP's height as I'm 6" or so shorter!. But I do like the Kia Soul, so if, as seems to be the case, it will be fine for you, that would be a good shout. 4140mm long means no probs fitting your available space, and personally, I'd prefer a higher seating position anyway, which the Soul has. You'd be looking at a 2018 car, but this would be comfortably inside your budget at around £11.5k from a Kia dealer. As such, this would also have the benefit of up to 5 years warranty remaining!. Here is an example for sale on Autotrader,

202010064686135

How much of the knee pain is down to the stop start driving as much as the car itself?

A smallish automatic may actually be as comfortable as a larger car. That would avoid probably a few hundred clutch movements and gear changes every day.