Alternative to potatoes
If you want a similar texture and flavor, I recommend trying other similar root vegetables. 

I use turnips and parsnips in similar applications. They're both dense, white and have a slight sweetness to them and they should hold up relatively well to long cooking times.

You might also enjoy yucca which can have a cooked texture similar to a cross between potato and banana. I've not tried them in this sort of application specifically but I think they should work.