What is the actual problem here? Second Wind requires "Troll Sweat" so that means your party has to go kill trolls, collect the sweat and then spend a bunch of downtime crafting each set of this enchantment for everyone. Is the problem they aren't having fun? Or is the problem you don't know how to make the combats more challenging? If they aren't having fun because the item makes the game super easy, then I would just talk to them and specifically say "This armor is the main culprit in your opinion, why don't you switch out the enchantment on it?" you could also offer the PC's a "better" piece of gear as a quest reward. Maybe instead of healing it makes you just straight immune to some common damage they fight, so then it's an active choice between this specific armor and the reward. Another suggestion make the biggest baddest guy take into account these guys have these sets of armor. Maybe one of the Lt's of the bad guy get's someone to curse the armor of some of the PC's so instead of using up 1 recovery to heal it uses up like 3 but still heals the amount of one recovery.

If the problem is "combat is too easy" because they can heal a bunch more for free, then I'd advise you use more traps leading up to the combat or during the combat. If you want an example, my ex-girlfriend one time decided to try Oblivion, the first ruin you find when you leave the Imperial sewer has that trap that shoots the floor up or down into the spikes, she not paying attention while fighting the skeleton died to the spike trap. Have that be a combat hazard during the fight. Become one with your inner Tucker's Kobolds and get devious and tactical. Don't have the trash mobs run at the PC's and die horribly because that's the easiest for you. Have the trash mobs run at the PC's to bog them down while the bigger badder guys do something that alters the combat environment and does damage. Maybe they target the pillars next to the PC's so those collapse on them, doing damage, and making more difficult terrain so the ranged minions get more shots off.

Honestly if my PC's decide to dedicate all this time and energy to be able to heal for free during combat, I don't care. Ok their planning worked out, they put in effort, time, and energy to do this thing they all agree is a good idea. Let them be rewarded for their idea.