It is important to try to get through as many battles as possible without losing any units, but I find it tedious to constantly right-click every stack to see if they are at full strength, and I've gotten burned a couple times by forgetting to heal a stack before ending the battle when I could've easily done so. I don't care how many hit points the "top" creature has, I just want to make sure that no units are lost, so that when the battle ends I'm still at full strength. Are there any options or anything I can turn on to make this easier?
When you click on a healing spell and then mouse over a creature, it will tell you how much health that creature will be healed, as well as how many creatures will be resurrected and also the max amount that could be resurrected.
This comes in the form of, for example, "100 7/13" This tells you that you'll be healing this unit for 100 health, which will resurrect 7 creatures, but this unit has lost 13 creatures total, meaning that after you heal it, it will still be missing 6 creatures.
This is useful especially if you have a mass healing spell, as mousing over one creature will show this information for every creature on your side (that can be healed).
A useful tip is on the turn that you could win on (or a turn or two before hand) pick your healing spell and just mouse over each unit you control to see if any are below their starting amount.
While you can see this information by right-clicking the unit on the field, it is kind of annoying to do so because you need to find each stack, and when you right-click the window stays visible, obscuring other stacks.
However, I've found that you can also right-click the picture in the turn order. Not only is this easier since all your stacks are right next to each other, but it is faster because the window disappears as soon as you release the button.
You can also press Alt+H to show health bars on all stacks. While this doesn't directly tell you if they've lost units, it is unlikely that a unit takes exactly the right damage to kill a unit, so any stack that has been hurt will likely show a health bar that isn't full. Obviously this will occasionally mislead you, so use at your own risk. =)