I don't think you should switch if you feel you need the four packs, you're going to be more inclined to eat something you shouldn't if you're hungry. Plus the losses aren't supposed to be much different between ss and ss+, you're still vlcd and in ketosis so you'll still lose. You're still on track for your stone a month so try not to worry about each week but look at what you've lost altogether. Keep going, some weeks you'll have bigger losses and some weeks smaller but you'll get to your goal if you stick with it.