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Angels are iffy. Nobody seems to really agree on what angels are, and I have found not many versions that are "gentle". I'm not sure what objective good is and whether it exists, but I think they're generally defined by being as strongly aligned with it as possible, which is often very much not safe and cozy. Your guardian angel loves you very much and has no absolutely no regard for your comfort if there is something of more import at stake.
Demons are obviously a bad choice. I mean, Sloth (Belphegor some call him) is often very gentle and harmless but that's because it's made out of wasting your life pursuing peace and comfort, so I'd stay away.
What remains is all kinds of worldly or "elemental" spirits. Those come in all shapes and colours, they're usually very strongly "about something". Maybe you'll find one that suits your criteria. I can't imagine such a thing being incredibly powerful though.
If you want to approach spirits and entities in general from a magick/occult perspective, you should be willing to "walk on the wild side".
A possible "safe and harmless" path is to work with some particular deities from within a religious tradition (maybe Pure Land Buddhism, because of its focus on devotional practice with the Amitabha Buddha, for example).
Thing is... He will help you with compassion and enlightenment, if that's what you want.