If you're driving the tank, literally any tank will work.
Quite a few prefer either a Paladin or Druid tank, due to ease in macroing their abilities.




For a healer, a Priest is really nice for PvE content.
Holy and Discipline are both decent, so its a preference between the two.

If your team doesn't have a Shaman on it, a Resto Shaman is a great choice because they're both a strong healer (AoE and Single Target) plus they bring Bloodlust/Heroism to the team.
Tremor Totem can break Fear/Charm/Sleep effects, even if you're Feared.

Stacking the Healer spec Monk is really strong, while leveling.
Not sure how they're at, at maximum level, but along the way 5x Monks is basically unkillable.
I don't know how two would be, but there's nothing saying you cannot play 2, 3, or 4.




If your friend was wiling to play 3x DPS, all the same class... and you had both the Tank and Heals...
That would be a full group, capable of a lot.

Lots of options.




I'd drive with the tank.

And use one of Grid + Grid Custom Layouts + Clique (all three addons) or Healbot or Vuhdo (both of these are stand-alone).
Each option is as good as the others, it is visual preference.

You want an alphabetical fixed order sort.
So the top frame refers to the same character on every screen, as does the second frame, etc.
The frames are positioned in the same place, on every screen... usually via Mouse Broadcasting to ensure they're in the same spot.

You place a Repeater Region over the whole area, with the Healer as your target.
When your mouse enters the region, broadcasting is enabled.
If you have the option to block local click (KVM Mode), use that... so your tank doesn't change targets when you want to heal.

Clique/Healbot/Vuhdo translates various clicks into specific heals.
I've used these before:
Resto Druid
- Left = Rejuvenation
- Right = Cleanse type spell
- Alt Left = Nourish
- Ctrl Left = Lifebloom
- Alt Right = Healing Touch
- Ctrl Right = Regrowth
- Scroll Up = Swiftmend
- Scroll Down = Wild Growth
My mnemonic was... Left/Right is default, Alt-Clicks are efficient, Ctrl-Clicks are emergency use, Scroll Wheel is AoE heals.

After a few sessions with the healer, whatever system you use will be natural.

I also like a couple that assist the main toon.
#show
<Insert Assist>
/cast [help][@targettarget,help][@targettargettarget,help] Heal Spell Here.

You can then have the Healer, heal whoever the tank is targeting.
And if that is a hostile, then the heal goes to whatever the mob is attacking (hopefully your tank).