Can you get to a circuits class? That will be a great allrounder in terms of weight bearing and cardio. Blooming hard work, though. There are lots of things along this theme though, things like body-pump, Kettlebells etc.
If you don't want to go to anything organised, I'd look to do 2 weight-bearing sessions a week (lasting about an hour - a class is your best bet on this, but you should be able to find a DVD that suits), and a third doing something else - running, cycling, tennis, spinning, riding.
Lots of weights exercises on the arms will help (press ups, tricep dips, pull ups, front rows - a Google should help point you in the right direction). For tummy, get planking, variety of cruches, but cardio will probably be most use. For legs, squats and lunges (plus the running/cycling/whatever).
I've always been naturally slim (not as slim as you though!), and have found since seeing a personal trainer for a year (see him weekly), I look much more balanced - toned where I should be, no more flabby jaw. It's been hard work, but the results are so worth it.