OK, so I have come to the conclusion that maybe it is time to retire my warm-but-heavy sleeping bag and cheapy karrimat since both are now well over 20 years old and were bought on an 18 yr old's budget then :)
I'd be grateful for any suggestions/recommendations. Basically, I don't do serious camping at all, very much weekends at events and the like - hence why I've not bothered replacing them.
But, I"m always walking/train/bike to where-ever I'm going, so I would really like to keep the weight and pack size down. Absolutely the best thing would be a bag & mat that would fit in a daysack or pannier with a change of underwear. I also tend to do my not-proper camping at random times of the year, not reliably in summer, so I think I need a 3 season mat/bag. Ah, and I have a bad hip, so a soft mat would be a fantastic addition, as atm I tend not to sleep at all well on my karrimat. The only positive thing is that I don't feel the cold and am happy to sleep in all my clothes for a week if needed 
Lots of people recommend the Fat Airic/Dozer mat, but they look pretty heavy compared to other options?
And would you go for a down or synthetic sleeping bag?
I don't mind spending a reasonable amount (planning for them to last the next 20 yrs), but not a fortune, IYKWIM. Any suggestions from the proper camping experts :)