How long you have had them or if they are worn out or not.
There are two basic styles of riding boots for English riding. Field and dress boots. Most dressage riders use dress boots while competing.
longer riding boots are better in my opinion as they make riding more comfortable for both horse and rider. Your appearance also looks much better with longer boots.
shoes with a small heel riding boots or jodphur boots are best
as long as they are strong boots
Riding boots are made out of leather and a saddle is usually made out of leather so both of them rub together whilst you are riding which causes it to 'squeak'.
There are several department stores like Macy's and Nordstrom that sell equestrian riding boots. Several retailers like Target also sell equestrian riding boots. There are also numerous websites that a person could buy equestrian riding boots from, some even offering free shipping.
There are many places to buy cheap women's riding boots. If second hand boots are acceptable, Ebay could be used as a cheap place to find them. Alternatively, Amazon sell riding boots. It may also be worth looking at your local stables as they sometimes have boots for sale.
Riding boots don't have grip because if you fall off and your boots have grip your foot will get stuck in the stirrup , because the grip will cling to the stirrup and you will get dragged.
Riding pants are to be tucked inside of the riding boots.
Jodhpurs are the trousers worn for riding, jodhpur boots are the short ankle high boots worn for riding. Riding boots (tall boots) and jodhpur boots (ankle high boots) can both be worn at any age, however if wearing the ankle high boots it is recommended you also wear chaps which fit around your calf giving you more grip on the horse. The advantage of the ankle high boots for younger children is that they are cheaper than the full riding boots and when a child is still growing rapidly there is less cost involved with changing boots as their feet grow.
a spur
Yes there are. Many of the basic shoe inserts can be fitted to a riding boot, or you can buy inserts made specifically for riding boots, either through the manufacturer of the boots or a secondary company that makes the inserts themselves.