I bought used cultus 2003 vxl recently, after some driving i realized the car oversteers at high speed on highway and used to get out of control in slight dissonance. When i got it checked i found out that its front tyres are bigger i.e. 175/70r13 while rear tyres were 155r13. Got them switched but now if i leave steering for a while the car drifts to left, now i found out the front left tyre is almost depreciated and it slides the car to left. I intend to change the tyres, not sure if i should change all 4 or front 2 tyres. The rear tyres (175/70r13) are only 4 months old and in good shape.

My options are:
1. Get front tyres of 175/70r13 and hence get all 4 tyres of same size
2. Get front tyres of 155r13 i.e. staggering with 155r13 front and 175/70r13 rear
3. Get all 4 tyres of 155r13
4. Get all 4 tyres of 175/70r13

My preference is to get good fuel average and smooth drive, when i searched online i read that rear tyres when have small size it consumes less fuel but to my prior experience i doubt that it will make car unstable at the same time i also think now that the instability of car at high speed was due to the depreciated tyre that caused the problem.

Please suggest me pros and cons of my options and suggest me the best option to get maximum fuel average.