Passive income is an income received in a regular basis with little effort required to maintain it. - Wikipedia
Having one source of income is dangerous, every OFW's should start building sideline business because economic uncertainty and unstable financial situations can have a big impact on your future. You can start analyzing the trend and check your strengths that could be compatible to your target passive income source.
At the moment, I'm focusing on building apps, rental properties and blogging. The good thing, results is amazing. I received a regular monthly income minimum of 50k combined those different sources. This amount should be reinvested monthly on other financial instruments to balance my portfolio.
First, Know your strength and use your skills. You should develop a skill. For example, if you are good in cooking, you might want to start selling cookies, muffins, skinless longganiza etc. etc.
Second, Be different and have a USP. Unique Selling Point is a key to attract customers. You should be different so it will be easier to sell your products. Every Friday my wife is buying cassava cake from this guy in the mall, his very friendly and he easily captured "suki" customers.
Third, Time Management. I know you are working full time but taking time to do a sideline business will be a training for you to become an entrepreneur. This sideline business can be a full time business later.
If you are looking for a budgeting app, watch this link https://www.youtube.com/watch?v=PIu1pXV4yyk