We launched https://emailoctopus.com around 3 years ago as a side project. The most difficult thing with launching a SaaS is the early days, where you've spent hours upon hours building the app and are only bringing in £400 a month.

We stuck with it though and today have a full-time team of 5 working on the app, are paying ourselves a similar wage to what we were earning in our full-time jobs and most importantly have almost complete ownership of our work-life balance.

I'd really recommend a SaaS business if you are after recurring, side revenue and as mentioned before https://www.oppslist.com/ is a great place to get some initial ideas. Your marketing skills will improve too - just stick with it for a year or so if you do go that route!