Why not buy a nice car?
For the cost of a C1 you can buy an awesome condition and good mileage Mk5 1.9 TDI. Still have a car capable of going more than 20 miles and 60mph. Running costs are very little between the two
I can understand the reason of downsizing or downgrading car but you need to weigh the benefits. Costs of selling the car, buying another, selling that after a year... can you not just put a bit more money towards the old mortgage now/cut down spending/stop modifying.. ?