Greetings, and thank you for your question! For most patients, Risperdal actually tends to be more sedating than Geodon, so yes, it definitely should help in that regard. It may even be better than the Geodon!
Also, while I'm not sure why your doctor is making the switch, another advantage to Risperdal is it is once daily dosing rather than twice, like Geodon.
Also, you do not have to take it with food like you do with Geodon.
All in all, it will probably be a very good medicine for you, with no need for an additional medicine for sleep.
You can also ask your doctor about "cross tapering" to make sure the transition is smooth and your sleep remains intact. In cross-tapering, you slowly go down on the dose of the outgoing medicine while concurrently increasing the dose of the new medicine.
A lot of information, but I hope this helps! Please let me know if you have additional questions.