A bit of advice for you if you are going to rent in France rather than the UK. It is not that different, but you should be aware.
Additional charges are often levied by car rental companies for:
-additional insurances, such as collision damage waiver are often charged
-listing additional drivers as able to drive the car may incur a surcharge on the cost of your rental
-Basic extras like a roof rack will usually incur an additional daily charge.
-You many have to pay for 'options' which might include air-conditioning (called climatisation or 'clim' in French, sometimes standard but not always); a CD or DVD player; a GPS navigation system etc. Your need for each of these will depend on your situation, but it might well be worth paying a little extra for in car entertainment or to help with direction finding.
-Car cleaning charges may be imposed - be warned!
-Don't go for airport pick up as it is usually more expensive.
Read the terms and conditions in your car rental agreement. There might be restrictions on how much mileage you can cover, how much petrol should be in the tank when you return the car, what kind of roads you are allowed to drive on (e.g. 'no off-road driving is included in the insurance' might include that car park where a tree falls on the car!) and others. Also check if you can actually drive outside of France, as I see you want to go to Spain and Italy - some companies won't let you take their cars out of the country. I actually did a similar trip last year, but just in France and I searched quite a few places for cars - the best I found in the end was these guys that do Mini rental in France
and as far as I remember they didn't have any restrictions on where you could go. I know that auto europe and elite also have minis for hire, but you would need to check their policies. But which ever company you go with, I don't think any amount of insurance will cover you to do this, but it might be fun! video Mini Cooper Ski Jump (Extreme video) - jump, extreme, ski - videos Ma-Tvideo France2
Finally, when you arrive to pick up your rental car be sure you have checked it for every little dent, scratch or missing hubcap so that there is no dispute when you return the vehicle. They are quite hot on this in France - take photos too if you see any damage.