I agree with Jeanette - if your Mum has a problem you might try explaining that you want to create something like Michelangelo, or Da Vinci - not something that could be included in "Girls Gone Wild".
That aside - I truly believe that the outline that you are looking for will actually inhibit your artistic development. You need to understand the structures below the skin to get the finished drawing to be believable. That is why many of posemaniacs daily drawing poses look like skinned rabbits! If you see the underlying muscles and tissues you know where a muscle bulge should be - where a bone juts out , and lends an air of authenticity to your work.
You can indeed concentrate on an arm or a leg, hand or a foot. In fact on Wet Canvas we had several threads on just one body part - there was a hand a day thread for a month, foot a day and eye a day - you'd be surprised at how much you improve (no matter where you start from) when you do these tasks in earnest.
So go for clothed models, single limbs or body parts - and work on your mother's perception of what you are wanting to achieve.
Just to let you know how much easier it is with a computer, when I first started figure drawing I had no idea where to find a local class. Female figures are easy to come across - there plenty of near nude, or swimsuit clad models in a variety of poses in women's magazines, and all kinds of ads. Men were a little harder. As I didn't have a computer (and NEVER intended to get one at that stage), the only way to get great poses in male figures (without it being a beefcake calendar) was to buy a particular Gay magazine here in Australia - all the pics are extremely artistic and usually very tasteful, but it still didn't stop my newsagent wondering what the &%& I was up to! He had a good laugh with me after he talked to my local Office Supplies shop owner, Denise, who used to do laser copies of some of my work, and he finally realised I wasn't a complete weirdo!
The things we do for our art
Just keep practicing the things that you can - get the details down in the extremites - hands and feet are notoriously hard - that's why so many artists leave them out or hide them as best they can. If you can work on them you'll be way ahead of the pack.
Good luck!