First of all it is dangerous to have wayward mats in the front drivers side, I had a 'generic' (non-Honda) mat jam the accelerator pedal once, very scary.
I wouldn't describe Jazz seats or seating position as being particularly uncomfortable, if you search for 'seats' and / or 'uncomfortable' on this forum there are plenty of threads about this with advice on resolving problems, you may just need to adjust the seat height, position and back-rest angle to suit you. I have driven many miles in Jazz MK11 and no problems.