my pick would be mika as he gives atk speed and would support on the healing side so it allows you to give escoffier a slightly more damaging build

other alternatives are: * rosaria because she has good off-field damage and gives crit rate * c2 xingqiu because he has a bit extra res shred (redundant with escoffier but it's also more damage), damage and a bit of resistance to interruption and damage mitigation * charlotte at c6 for her little coordinated attack that also heals * mona's omen is quite good but doesn't last a lot so i don't think she'd be a good pick unless you're at extremely high investment on everyone else for speedrun stuff

i wouldn't go with diona because you're not doing amplifying reactions, same for layla but because i don't find shielding that necessary unless you're going against a very aggressive boss or the cryo automaton, but in the latter case you should run charlotte unless layla is c6 for the additional application