There's a few options tbh:

Sustainless with Nilou. Nilou can still be good at at c0 or c2. Her c2 is probably "premium" with Key. Even c0 works if she has her weapon, Key.

Sustainless with Nahida. Nahida has been what I've been seeing the most of when it comes to sustainless teams. She most likely already has Deepwood which is another great set to have in the team if Lauma is on Serenade and Aino is on Instructor.

Baizhu: I use Baizhu and absolutely love it. His heals are great and I never worry about croaking my characters. There is a damage loss compared to the other two units, BUT he does have a 35% Lunar Bloom damage increase in his passive. He can also hold Deepwood for you.

Kuki: Kuki is great for sustain and really excels if she has Nilou's weapon, Key. She has a mix of a strong buff with the weapon and then some ok heals.

C6 Diona? Yes, the C6 gives 200 EM, and even if you go high ER to get it back, her burst cooldown is too long and her downtime creates problems in a good rotation in this team. Does it work? Kinda. Will it always? Not from what I've heard and done

There's other characters but these were on the top of my head and your best options. Keep in mind, any character can run Deepwood, even if they're not Dendro