>>366760
Banana will be too soft. You'll crush it and it will be an unpleasant mess. Frankly, nothing around the house is going to have the right combination of flexibility and firmness. Nothing you can make, either. Your only real options are to risk buying a proper toy, stick with your fingers, or use a penis.
The only thing I found while I was experimenting that made a passable toy was part of one of those telescoping lightsaber toys. I unscrewed the handle and took out the top blade section, and while it was too rigid to be ideal it was serviceable until I got a horse dildo.
I still live with family too but I've managed to hide two dildos and an onahole from my family for years now. My father works from home so there's essentially no time when I'm here alone, and I still managed to get my hands on them. IMO the bigger difficulty is not getting caught using them, rather than not getting caught acquiring them, and the former is something you'll be dealing with even if it's homemade. I recommend going for something meant to go up your ass if remotely possible.