Jodhpurs

While you can make do with an old jumper or rugby short on the top half for riding, the same isn't really true of the bottom half, and jeans really won't do. They don't stretch, they are cold, and even colder if they get wet as they don't dry quickly. What you are going to need to make your riding comfortable and enjoyable is judhpurs.

These usually come by waist measurement rather than traditional dress size, but always make sure you try them on in a tack shop as even with waist measurements, sizes seem to vary a lot between different makes. They're also fairly easy to come by on ebay, but again, make sure the sellers checks the waist measurement for you.

There's also a difference between jodhpurs you wear in the summer, and heavier ones for winter. While you need thick, warm jodhpurs for the winter, in the summer you'll be swealtering. Get some made from a cotton base. The best jodhpurs I've ever bought for summer came from joules, and were in fact breaches rather than jodhpurs. These tend to be more comfortable as on the whole they arn't as tight and give you more room. By the time it gets to winter I'll be back in warm jodhpurs again. Avoid some of the cheepest nylon ones though - they don't feel good, and tend to make you sweaty rather than warm.

Wellies and boots
Riding hats
Riding jackets
Saddle up