Best filter for 1.5 g betta tank

I CANNOT convince my mom to get at LEAST a 2.5 g tank for her betta. Doesn't matter I'm 36 and have worked as an aquarist intern. But we're having issues with filters for her. One it came with has too strong a flow. Tried a sponge filter but it's doing nothing to help. Next filter I tried broke when opening it. I looked at Petsmart's Betta filter (Top Fin® BETTAFLO™ BF5 Low Flow Filter | fish Filters | PetSmart) and it looks nice except it has no sponge filter. If there's room I'd be willing to boost it up with proper biological filtration but I don't know if it HAS room (and I've never done it before... could use some guidance). Otherwise, I want an adjustable flow. Her betta is very sensitive to flow. What's the best to get and do? I've given up going it by myself. Thanks in advance...

 

Might be able to put a part of a plastic bottle on there to baffle the flow some?

 

is the filter in question a HOB? If the betta is that sensitive to flow, I'd just ditch what you have and put a small air-driven sponge filter into the tank. Bubbles from an air tube are about as gentle flow as you can get. Might be a bit cramped but that's better than too much flow or no filter at all.

 

I’ve heard of making tiny diy sponge filters.

 

Tried a sponge filter but it's doing nothing to help.

What do want the filter to do that a sponge filter can't do?