Thank you everyone... for replying.

I don't think it's going to be something, that I can understand without a little more experience.
At the moment it's all just gobbledygook. Bike stores and the people who run them are great and all.
But if you want to do something inexpensively... and you don't have the knowledge,
there isn't a lot of options out there. Bike sizing is a mine field of different scales and formats.