I also burn wood exclusively for heat. I split with a 8lb maul. Sometimes you get really knotty pieces but over time you learn how to split them by looking at the grains and where to hit. Aim for the side with out the knot and take corners off with the maul. Eventually you will have a chunk thats all knots. Put that aside for what I call an 'all nighter'
You will just be wasting your time with a manual splitter. Waste of time, money and energy.
What does concern me is how would one burn wood post SHTF? No gasoline = no chain saw to buck logs. Using an axe or saw to cut up wood would be very time consuming and a full time job within it self. Would also need to get a couple mules to drag logs to the house.
To me... Its impossible to plan for permanent SHTF. My only real strat around this one is to always have wood on hand before such a situation. Stack it in the spring, burn it next winter. Stocking wood for longer then 1 season is pointless, it drys out too much and burns too fast.
This last season I went to pre-split. I spent so much time, gas, energy last winter that it wasnt even worth it to get log length and split it myself. I got better stuff to do then waste all my time bucking, splitting, stacking, carrying wood up to the house.