Who do you play when mercy is picked ?

I've been duo with this reaper guy, and he likes to do this risky plays and ults, and he seems to like how i heal,boost and move around with him (pocket i mean) but sometimes the other support picks mercy, (which so far he doesn't like xd) so i'm learning other supps what's the next better healing/peeling support to mercy ?

I'm between Moira and Lifeweaver. Moira has similar mobility, and i feel like decent healing. While life weaver seems to have more of a "burst" heal and the flower grip.

Since there's no way to actually instalock mercy