If you like tinkering, then a 140k car at your level of usage should keep you occupied on the weekends without keeping you off the road.
A 140k T/Spark donkey will be fine, so don't worry about it as long as the cam-belt and tensioner have been changed recently. The water pump might be my main concern.
However, there's a service interval requiring a cam-belt/tensioner at 144k.. so that would be a good time to change the water pump and variator too (and it's probably why the 140k car is cheap).
Also look at the spark plugs since you're likely to be at the end of the life of the second set. A set of 8 platinum-tipped plugs is north of £65 (£80 depending where you buy them).
The rest of the car will be starting to sag a bit too.. so do the normal "car" checks on the radiator, gearbox, shocks and steering etc.
If you don't like tinkering go for a 68k job since the ancillary bits and pieces will be in better condition, though you still have a cam-belt service coming up (72k).. though water pump will be fine and maybe the variator too (unless it makes a diesel noise on tickover).
Forget the diesels at your mileage. Go for gasoline..!
Diesels are good and reliable.. but they'll be dearer to buy and as expensive to run.. since the ancillaries wearing out is the biggest cost on cars that age. A good petrol, with new belts/tensioner/pump/variator (and plugs) will do you..