Do what you want to do, but for pete's sake don't go around assuming that everybody in the world is going to be pleased by "I'll pray for you." During my own serious illness, I'd respond to that with "If you can't do something REAL for me, like bring me magazines or help me with laundry, with errands, with pet care, then just don't bother doing anything. Take your freekin' thoughts and prayers and stick 'em up your nose."
It's not that I minded someone praying for me. I'm not a believer, but if you are and you want to pray about me, it's nothing to me either way. But don't tell me "I'll pray for you" as if you're doing me a favor. I didn't ASK you to pray for me and I'm not going to THANK you for it. To me "I'll pray for you" is saying "Seeing how pious I am?" and only brings to mind Matthew 1:1-6.
Be careful not to practice your righteousness in front of others to be seen by them. If you do, you will have no reward from your Father in heaven. So when you give to the needy, do not announce it with trumpets, as the hypocrites do in the synagogues and on the streets, to be honored by others. Truly I tell you, they have received their reward in full. But when you give to the needy, do not let your left hand know what your right hand is doing, so that your giving may be in secret. Then your Father, who sees what is done in secret, will reward you. And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by others. Truly I tell you, they have received their reward in full. But when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you.