We don't commonly say '사랑으로' or any phrase with -으로 when closing a letter. We typically close a letter with a phrase containing our name, like "XX 올림" (if it's to someone older", "XX 드림" (not as respectful but still formal), or just "XX가" or "XX"(between friends). I would just add something before one of these phrases. So if your first name is XX, you might say, - 당신을/선생님을 사랑하는 XX 올림 (the most formal) - 당신을 사랑하는 XX 드림 (medium formal) - 너를 사랑하는 XX가 (informal, like to a close friend - '가' is optional) (The '-가' at the end can be understood as a shortening of 'XX가 보냄', i.e. I, XX, am sending the letter.) To make it more interesting, you might add the place where you're writing from or other relevant things, as in: - 서울에서, 널 사랑하는 XX가 (With love, from Seoul, XX) - 다시 만날 날을 기다리며, XX가 (Waiting for the day to see you again, XX)

I would say 사랑을 담아, OOO 애정을 담아, OOO