I used a 500g packet of dried cannellini beans for this, but you could use any kind. Can I leave it to you to be responsible for choosing how long you soak and boil them? The instructions on my packet pointed their finger right in my face and said sternly, "don't put them in a slow cooker unless you have soaked them for a minimum of 8 hours, and boiled them for at least ten minutes". So I put mine on to soak on Thursday evening, before I went to bed. They must have soaked for maybe 20 hours by the time I dealt with them on Friday teatime. I boiled mine for 30 minutes, before cooking them in my slow cooker on "high" all night. My slow cooker is very gentle. I could have boiled them for 90 minutes (as per instructions) THEN cooked them on "low" all night. But I wanted to get them in the pot and on the go as soon as possible so I could lounge around.
In another pan, I fried and softened a chopped onion, chopped garlic, and some sliced carrot. Later, I added a jar of tomato pasta sauce (marinara sauce?) and a tin of tomatoes, a good sprinkle of herbs, a couple of bay leaves and a big grind of pepper. I think this formula is pretty similar to Greek-style big beans. NO salt at this stage, apparently it can prevent your beans cooking properly. Salt goes in right at the end. When I mixed the sauce and beans together in the slow cooker pot, I added a dash more water, just to make sure all the beans were submerged in liquid.
So it must have had more than 12 hours, simmering and bubbling gently all night. My slow cooker is very good at not allowing steam to escape, but if yours does, maybe put more water in.
And, in the morning, I had this lovely pot of hot, tomatoey, thick, slightly sticky big fat soft beans. I tasted, and added salt and a couple of pinches of sugar. Personally I have to have an egg with mine, and I had it all on a chapati, because they were what I had.