Firstly let me clarify, (sood) bank interest is haram in the first place. So your option would be to invest in the profit/loss Islamic sharia abiding savings account, which unfortunately do not pay good profit. They pay you peanuts, you will get more money if you begged in the streets of blue area Islamabad than you will gaining any decent profit from there.
You can possibly gain good monthly income in investing in a franchise catering fastfood takeaway / eatery. I have seen a lot of big name brands (i.e: kfc, pizza hut, mcdonalds) etc... That are very busy and making a lot of money. This would provide good monthly income, but you need good money to invest in the place. You need a good busy location also.