Xero or Quickbooks Online should work fine. If you ever outgrow them you can always migrate your data to another system.
The main difference specific to SAAS is accounting for deferred revenue. You can always hook up something like Chargebee to Xero to get better reporting in that regard.
Unless you are an accountant, your time spent on accounting rather than growing the business is low ROI. The same is true of freelancers, etc. If rates don't cover basic business expenses, the long term prospects are not favorable.
An accountant is an off the shelf solution.
Good luck.