Freelance app developer.
I'm serious though. You've got the right background and have coded before.
The beauty of apps are they often tend to be much smaller than desktop apps or websites so it's often a one man job. It can take 1-12 months over one-many versions for the client to get to where they want to be.
Once completed you can start charging a maintenance/support fee. After several projects these start adding up.
Typically you will write for Android first and then port it to iOS (development tools dependant, I've told you what I use) and often it involves a cloud server (I like LAMP or LNMP). You can pick up some of these skills in a few weeks with Lynda.com for example.
I get more enquiries than I can handle and turn off my Google advert while on a project. Though it's easier if the client is in your city it's certainly not a requirement. I advertise in all southern african countries. Adverting is less than R1,000 a month.
Oh and you get to work from home or a coffee shop.
You'll be able to do this for many many years to come. Apps aren't going anywhere.
Pm if you want to chat.