Hi there,
Welcome back to the Community. I'll be happy to guide you in the right direction so you can convert from Sage Business to QBO with confidence and ease.
Aside from using a third-party data migration app, you can convert your Sage 50 data using the steps provided in the following article that provides more info about: Converting Sage 50 data to QuickBooks Online. The article provides in depth info as to what type of data you can convert and how. That said, you're welcome to reach back to me here in case you have additional questions. Otherwise, if you decide on using a third-party data converting app, I recommend searching for one on our site www.apps.com.
Let me know if this info helps by leaving a comment below. I'll be a message away in case you need anything else.