I'm going to tell you a few ways to get bells easily In WW.
Hoarding: When you find items store them in your house and sell them when you think you have enough.
Fishing: Buy a fishing pole from Tom Nook and catch fish. This can earn you bells quickly if catch big fish.
Bug Catching: This one is kind of hard because the bugs move fast and you can't move while swinging the net. If you catch a decent amount of bugs or a few rare bugs, you can make decent profit.
Trading: Trade with other people over wi-fi for expensive items/furniture. Some of them can be sold at a high price.
(there are other methods but these are the ones I know, hope this helps pay off your mortgage.)
I'm too lazy to write a signature right now, I think I'll make one tomorrow. Then again, maybe I could make it after lunch.... Nah! Gonna make it tomorrow.