I've gone with:

1x Blood DK
1x Arcane Mage
1x Desto Warlock
1x Resto Druid
1x Resto Shaman

The composition doesn't have the simplicity of double Shaman.
But I like having Wild Growth and Rejuvenation stacking across the team.
Plus Mark of the Wild across the team, and Thorns on the tank.

Still tweaking one button spam for the healers.
Shammy can Lightning Bolt indefinitely; Druid can Wrath forever.
Glyphed, innervate is 50% mana on the Druid and 100% on the Shaman.

Possibly run one healer as a main healer, via Repeater Regions.
And the other as a passive heal boost / support DPS.
But I like both healers with a healing and DPS rotation that is mindless.