I spent 5 years trying to get a micro ISV off the ground which made scheduling software for hair salons. It was a terrible idea for a large number of reasons (described in detail here: https://www.jasonswett.net/im-shutting-down-snip-heres-why/) and I never made more than about $430/mo.
My opinion now is that info products are a better way for a solo founder to get started with a product business. The reason is that a SaaS product can take a huge amount of effort (perhaps pre-traction effort, which is risky) to get off the ground whereas an info product business can be started with a tiny "guide" and then expanded outwardly from there, keeping effort in proportion with traction the whole time.
My current business is AngularOnRails.com, an info product business. In its third month of making money, it made $1580, over 3 times what the SaaS made at its peak. Here's a detailed income report: https://www.jasonswett.net/november-2016-angular-on-rails-in...