Hello...I have been playing piano "by chords" now for years, but there was a time when I couldn't play a note without sheet music in front of me.
My advice is to learn (if you don't already know) the number of steps between notes in both a major scale and a minor scale. There are whole steps between each note in a major chord, except between the 3rd and 4th, and the 7th and 8th, where there are half steps (this is easily demonstrated if you play C major scale on the keyboard). This will apply to a scale in ANY key you want to play it in.
The same applies to the minor scale (play A), as all the half steps are naturally played on the white keys, just as all the half steps for a major scale are shown on the C scale. Then you can apply this equation to any key. (the half steps are between 2nd and 3rd, and 5th and 6th)
I personally almost always use a 1st, 3rd and 5th for a chord. Then you can change it by using a 4th or 2nd for suspended, adding a 7th, etc.
Hope this is helpful