My players want extra effects from their attacks. What should I do?

I’m DMing for a group of 4 players. Two of them have played a fair bit of 5e before, and two of them are new. I’m also new to DMing, though generally familiar with the rules of 5e.

One of the new players is trying to get creative in combat, which I think is great! The problem is I’m not exactly sure how I should adjudicate some of her requests in a way that won’t break the game. Some examples of what I mean:

Can I make an unarmed strike and use my talons to scratch the enemy’s eyes and blind them?

I attack them in their Achilles’ heel and cripple them so they can’t walk?

Now I know that the RAW answer is "No, you can’t try that." But that’s such a boring answer and I really hate to feel like I’m shutting down anything that isn’t just plain and simple attacks. In general, any time I say "No, you can’t do this", I feel like I’m shutting down my players fun.

Like I said, I like that she’s trying to be creative in combat, but if an unarmed strike can potentially blind an enemy, that’s incredibly strong. And if the PCs can do this to enemies, it’s fair game for enemies to do this to PCs as well. I can think of some house rules to balance it off the top of my head (Higher AC to hit a small target, enemy can make a constitution saving throw to avoid the effect, etc.) but I don’t want to worry about proper balance while we’re in the middle of a combat.

What’s a good way for me to empower my players and make them feel like they actually have these choices in combat rather than shutting them down, but without breaking the game?