Hello Paul, and welcome to the forum.
Bushes are mostly specific to each kit.
If just starting out and you like a particular kit, buy a good number of those kits and buy the bushes to suit that kit. That will spread the cost a wee bit.
Label them in a container as Eamonn suggests.
When you move on to another kit same again.
As time goes on you may move to just using calipers, like Mark above.
Alan