No point in splashing the cash on proposed suspension upgrades until you get rid of the ditch finders.
Perhaps you may find that the handling characteristics of the car will become acceptable to you once you have done this without any unnecessary expense.
Also driving tuition may be a very good plan.
These guys are good: http://catdrivertraining.co.uk/
If after that and you are still looking for improvement then the items listed below would help.
The list is not exhaustive, but it is a starting point after you have addressed the tyre issue.
Reduce the weight of car:
Reduce the unsprung weight.
Fit fully adjustable coilovers:
Fit adjustable geometry arms:
Fit suitable adjustable sway bars:
Fit adjustable drop links:
Replace bushings as required:
Carry out a full 4 wheel geometry check and adjust to suit your needs.