Computer packages for generating invoices - small business

Hi. I'm after some recommendations. I have recently started work for a small private medical practice. At the moment the invoices are all produced individually and just typed into a template. But my boss (and I) would like to move to a system where the contact details of clients and room users can be stored and invoices easily created from them using the invoice number format we already use. I have used Sage One. But even though I know it can do this, there is lots of other stuff we would not need (most of the accounts are done externally and the basic bookkeeping is done on a spreadsheet) so it would be an expensive option. Obviously security is also important in whatever we use if it is cloud based because of client confidentiality.
Does anyone know of any cheap (or free) packages that can do this?
Thank you.