That Paul calls something a matter of individual conscience does not mean that you are free to use the way you feel about it to decide what to do. For such matters just as well as for others for whom Scripture unequivocally has one moral rule for all people, feeling good about a certain course means nothing. That a matter is the former means simply that we, having different understandings of Scripture and ourselves (and we try not to fancy ourselves better than we are), will arrive at different decisions.
If understanding of Scripture is the same between two people, however, then whatever difference in the way they should act is due wholly to differences between the two people that can rationally be said to bring to bear directly on the question at hand. If not, differences between people are not a factor at all, only an excuse for people to act as they wish as long as their consciences have insufficient hatred of what is bad.
It is sloppy to pick the thing we like, check quickly and find that we don’t feel bad immediately about it (or some may say “feel peace about it” as a defence), and then do it upon that basis. It’s not a question of how fastidious you are, or how diligent to do the right thing, but of how important Scripture is. The way you act will be what you really believe, not what you wish you believed whole-heartedly.
To keep a clear conscience, then, is just not to do anything that makes you feel remotely guilty and not to allow people’s approval or disapproval per se to determine your actions in spite of what you Scripturally believe. You may want to protest, “But I’m an INFJ!”, but that’s the way it is: Scripture does not allow us to make moral decisions on the basis of transient feelings, without some hard work.