Hi Bob, 

It is perfectly normal to have some trouble nailing down those basic chords, with all their notes. 
But I would strongly encourage you to stick with it, with the goal of getting those basic chords under your belt. 
Take your time, but hold onto that goal. 
The easier variations you suggested are all lovely chords in and of themselves - and may work nicely in certain contexts, with certain songs. But they are not considered direct “swap-outs”, because as Bill mentioned above, they will necessarily have a different sound and mood than the “full” chord. 
A C chord sounds different than a CMaj7 chord. D sounds different than Dsus2. 

enjoy the variations, but also, keep working those basics! 
you will get them, I have faith!

- Lisa