Numbers are my jam (I'm an accountant) and I had tried using a spreadsheet, along with a binder for all the soaps I had made and a notebook for recipes, but it was hard to keep it all organized, not too mention that I'm not an advanced Excel user. Another soap maker recommend SoapMaker3 and it's a bit of a PITA to get started if you've already been making soap for awhile and have a couple of shelves filled with colarants and scents, and other assorted things. The program does get you started with a few basic things and gives you a nice list of oils and butters to choose from, but you have to enter your colorants, scents, additives from scratch. But once it's in, it's in and then it's just a matter of keeping up with it.
I started with the Lite version because I wasn't planning on doing only sales for a while yet, but recently upgraded to Professional because I really need to have a reliable inventory. Especially since I just discovered that I have three bottles of Lemon Verbena and bunch of other duplicates and triplicates. So I'll enter my recent purchases and then print out my inventory sheets and do inventory and update.
I'll also sit down with my binder which has a sheet for every batch of soap I have made, but I will only be entering the ones that turned out well. It's more about making notes on scents, colorants and what not. Actual soap and lotion bar inventory will be limited to what I have made in the past month since I took a few months off.