I'm short 5'2" (1.57 m) and 247 lb (112 kg). I've been working to lose
weight and have come down 5 st (30 kg) so far. Now I really want to
ramp up my exercise and was looking at cycling as an option.
I've tried looking on websites for advice
but can't see something simple I can understand.
I need some advice on suitable models that would be a good first time
purchase. I'm clearly not going for speed and adventure just yet,
so something basic that will fit my size and weight.
A used women's hybrid would make a good "starter" bike for you: a beginner, focused on physical fitness, who may be experimenting with different types of cycling to discover what you like best.
Why a hybrid bike? Versatility. A hybrid is suitable for cycling on crushed gravel or paved surfaces (bike paths or streets) without really being ideal for either one. That is, a mountain bike is best for off-road, and a road bike is best for paved roads, but a hybrid combines aspects of both in a general-purpose bike.
Why a used bike? Hedge your bet a little. If it turns out that you dislike cycling, a new bike is wasted money. If you like cycling and want to keep doing it, you'll probably buy a better bike (or two) once you discover which type of cycling you prefer. Your second bike-- road, mountain, etc.-- is what you'll want to buy new and put your money into. Many bike shops sell used bikes in good condition, in some cases because the previous owner wanted a better bike or didn't like cycling enough to keep riding.
Why a women's bike? A women's bicycle is built for a woman's body. (For example, a typical woman has longer legs and a shorter torso length relative to her total height than a man.) A woman's bicycle allows for these and other differences to make her cycling more comfortable and efficient, which probably improves the odds she'll enjoy and keep doing it.
My advice: visit your local bike shop, explain what you're looking for, and take a few bikes out for a test ride until you find one that feels good. Take your time. If they don't have what you're looking for, try again when they have more used bikes in-house, or try a different bike shop. If you get any sales pressure steering you toward a high-end bike or equipment before you feel ready, leave.