Same system with a few additions:
Pick the skill level necessary for the task. If the character meets it they get a +1, if they have double the skill or more a +2. If they don't have the required level they receive a -1 or -2.
Do the same with a characteristic level if desired (for example if they are shooting and have ADM or ASM for their weapon).
Total all mods.
If the total is 0, roll 2d6.
If the total is positive add that many dice to the roll. Roll and take the two highest dice.
If the modifier is negative add that many dice to the roll and take the lowest two dice
A '2' is a catastrophic failure with possible adventure derailing consequences.
A '4' is a failure with extra penalties. You use up resources, are delayed, or break something.
A '6' is a success but it has a downside. You make the shot but exhaust your ammo or jam your gun. You stabilize your injured friend but expose yourself to attack etc. You can take it and bear the consequences or take it as a failure and try again. It could indicate success at a routine task with a slight delay.
An '8' is a plain old success.
A '10' is better than average with some small benefit derived.
A '12' is a exceptional success. You succeed with a big bonus, like shooting the gun out of the bad guy's hand or finding just the right information on a research run etc.