What's your succession law? Can you change it? I'm guessing you started in 867 as Bjorn Ironside. You probably don't have at least 3 holy sites to reform the religion if you have just stayed in England. I'm guessing you're also gavelkind as unreformed Pagan. One trick is to marry an older woman over 45 so she can't have kids with you but you can share half her stats for your state attributes. Have a kid with a concubine. Get rid of the concubine after your first kid and then only have bastards. If your first-born dies, legitimize the best bastard so you won't have a succession crisis. If you only have one legitimate heir, your kingdom won't get divided up on succession. You can also convert to Christianity so that you can get different succession types. It should be easy to convert where your at. There's other things you can do but those are the most straight-forward.