I have had bookkeeping clients come to me with the old ledger system and I am just blabbergasted.
Can you run your business that way? Yes, of course. It was done that way for longer than it wasn't but believe it or not it is costing you time.
Now, I don't know what you mean by "expand" when you say you do not intend to expand your company. Do you mean you do not intend to grow anymore than you are? Or just that your not looking to add levels to your company, your not trying to become some big ol' franchise...
If you truly meant you are not trying to increase your revenue, clients, ect. Frankly, and I will hate myself in the morning for saying this, continue on with what your doing. It's working for you, you are not going to be growing as a company, move on. I really hope that is not the case though.
If you do want to grow, you really do need to take a step into the digital world. There are plenty of places to get help, free or otherwise. You don't need some expensive bells and whistle program but you do need a basic accounting software that can ideally download transactions from your banking website and pump out some reports for you.
Best of luck,