Welcome to the forum.

Best thing to do is have a look through the pictures forum and have a look through the old picture posts for sizes.

After that do ALOT of research so you know everything possible. Just reading through most of the threads on here will be pretty much all you need to know.

If you and your mum do decide to get a Ball Python then make sure you get the enclosure set up before you buy your pet. This can take up to a week to set this up properly and it will save you and your pet alot of stress and heartache.

Just remember if your on a tight budget then housing in plastic tubs is common practise on here and also can save you $$$ and they are alot easier to get the temperature and humidity in the tank spot on.

Make sure your mum knows that if any thing goes wrong with your pet medically vet fees will also be needed. Not that it happens often but just incase.

Feel free to post any questions you like but try to have a good read through and learn what you can yourself first.

Regards

Jim