there are several estate cars with similar sized boots (or larger) but it's more likely to be what is available for the budget in the current inflated (albeit falling back) market, in what condition, & does it need to meet LEZ etc. standards or other requirements.

However, you could start by looking at Skoda Superbs.

While it is very easy to find the boot capacity in litres, it isn't so easy to find those actual dimensions. But even looking at estate cars with a comparable boot capacity isn't that easy because a 2005 Passat could be either of two generations, because that was the year the B6 replaced the B5. That matters because the B6 had more than 100 litres greater capacity than its predecessor.

As for easy on the eye?, beauty is in the eye of the beholder. A car you like the look might be repulsive to me or vice versa!.

I'd be interested to know a bit more detail on what you mean re the bodywork being shot?. The body panels are hung over the frame, essentially just to keep the weather out. It is the frame which provides the strength, so as long as there are no exposed sharp rusty edges, it shouldn't be a problem. If the car is still sound mechanically (and it sounds like it is), I think I might be inclined to spend a bit of your budget tidying it up and just keep it. Partly because in todays market, £5k wont actually go that far, but also because, "better the devil you know"!