Glad to hear the cat is all shut out
Upright wheels are a must for Syrians. They are better for their backs and allow them to run most naturally. You can also put in a flying saucer if you want, but only in addition to an upright wheel.
The best wheel in my opinion is the 12 inch silent runner. You can buy it here:
Silent Runner 12" regular wheel | South West Sugar Gliders
And if you want you can attach it to the cage wall with this:
Silent Runner Cage Attachment | South West Sugar Gliders