Going off of Knights that I already have, the best I've cobbled together so far that doesn't lean heavily on winning in the first round (i.e., Dendrobium and four boosters) is Acacia (New Years) as the foundation followed by four of RG Kale, Japanese Anemone (Relaxed Queen), RG Dahlia, Habranthus and Lotus (June Bride):
Acacia (New Years)
- +130% attack for self
- +130% attack for self in boss fights
- +160% damage dealt to bosses by self
- 1.28 to 1.36x skill proc
Acacia lacks crit on her own but otherwise is ready to deal big damage.
RG Ornamental Kale
- 1.2x skill proc
- +32% attack
- +magic coverage for three Knights including Kale
- +20/50% crit rate/damage
A solid source of crit damage with a decent crit rate bonus as well. Skill proc is never bad to have and +32% attack is a solid bonus. The magic coverage is good or bad depending on whether or not Habranthus also ends up in the squad (i.e., coverage overlap).
Japanese Anemone (Relaxed Queen)
- +30/60% attack after one/two turns
- +30% defense
- 2x skill proc the round after being attacked
- +30% damage the round after being attacked
The Queen can build up a lot of damage boosts even if she gets burst down early on, but ideally she stays alive long enough to trigger multiple skill proc boosts.
RG Dahlia
- +30% attack
- -20% pest attack
- +30% attack in boss fights
- +25/30% crit rate/damage
- 1.2x skill proc
The second source of crit bonuses and a few attack bonuses to help increase Big Boss Acacia's numbers as well as a pest debuff to soften incoming attacks.
Habranthus
- Heal one attacked squad member by 15% after an enemy attack
- Heal the squad 30% every three turns
- Negate damage once for each squad member
- 100% counter with attack equal to 450% of defense
- +hit/pierce/magic coverage for three Knights including Habranthus
Lotus (June Bride)
- Heal one attacked squad member by 15% after an enemy attack
- Heal the squad 30% every three turns
- +20% attack
- +25% attack in boss fights
- 1.28 to 1.36x skill proc
- +15% skill damage
Two flavors of semi-regular healing with slightly different approaches based on their other abilities. Habranthus is slightly more defensive (one-time negate) but has type coverage and counters; Lotus has three flavors of damage boost along with more skill proc.
Overall it's not great (among other things crit rate isn't maxed and Lotus is the only source of +skill damage) but it's a start.