A man after my heart - SOPs - why successful companies keep trudging along. Process-dependent over people-dependent.
I use to simply use Word to write SOPs for clients but now use Quark, a publishing program that allows one to setup format and insert pages, etc. - but not something I would recommend for a novice. I`m sure there are lots of SOPs programs out there but I can not vouch for any - sorry.
But good for you for getting started on this at an early stage of your business. Years down the road, you`ll be really glad you did. Just keep doing it - don`t stop the practice.