Choose only such friends that you can trust.
Is using that in above sentence incorrect? A friend suggested to use as in place of that but I think that is horribly wrong, although replacing as with whom seems feasible but I think even that is fine.
I think both are wrong actually (although your meaning would be understood, I’m just being picky). I think I would actually say “as”. A formulation with “whom” might be “Choose only those friends whom you can trust”.
For me, the use of “such” implies “as” because it qualifies who is included in the “such”
As phrases go, its possibly straying into being an archaic format but that’s just the way it sounds to me. It feels like something that would be said in an 18th century novel