I suggest you get on Discord and join SWTOR Theorycrafters. It seems like that is the place to go for all class info these days. This is what they have to say about Merc/Mando healers and its worked great for me so far:
Set bonus: Concentrated Fire; one piece Amplified Champion
Tactical: Rocket Fuel Vapors
Amplifier: Medtech
Stat distribution:
• Alacrity:
>= 1213, 1.4 GCD without Guild Perk
>= 1895, 1.3 GCD with Guild Perk
• you can also go for the 1.3 GCD without Guild Perk:
>= 3208 without Guild Perk
this choice should depend on your personal playstyle
• Critical: remaining tertiary stats
Hope that helps. Cheers!