I'd rather say "mich auch" (who does it make feel schön? - mich).
/I don't know what's going on with the downvotes, but not a single German would reply "ich auch" if someone says something like "Das gibt mir ein gutes Gefühl" (what would be kind of an appropriate translation for the sentence above).
I (subject) do something. - Ich (subject) auch. (correct)
It makes me (object) feel good. - Ich (subject) auch. (wrong)
I usually translate ihr as "you all" except when it's obvious from context, like in "You are men" ("you" can only be plural here). It's an accurate translation while not sounding too Southern. And if the ihr is particularly informal, then I get to use "y'all" as an extra layer!
"Bist" and "Sind" are both conjugations of the verb "sein", meaning "is". The former would be for INFORMAL 'you' and the latter for 'we', 'they,' and FORMAL 'you'.
You just have to learn them by heart. Though there are usually rules, "sein" is an exception. Search if you want to find out the conjugations.
Bist is for the singular and sind is for the plural but only when you are reffering to yourselves, for example Wir sind (We are.) Seid is also for the plural but only when refering to other people, other than yourselves. For example (Ihr seid) or as it is in English (You all are.)
That means the same as "Du bist perfekt", whenever "Sie" refers to the one you are speaking to. I would say "du bist" only to a friend or to a child. To all others I would say: "Sie sind". To two ore more people I could say: "Sie alle sind perfekt." But would I really say that? If "Sie" is the first word in a sentence it also could mean they, because then "sie" is also written with a capital S. "Sie sind perfekt" could also mean: the games are perfekt or the holidays are perfekt or some other things.