40" 1080p @ 3 feet away sucks! You need 4k for this.
but...
Y do U sit 3 feet away from a 40" screen?
How old r u anyway?
If you are sitting about 3 feet away, you will like 24" with at least 1080p or 1200p or 27" with at least 1440p.
But ask your parent before you buy a monitor/TV, I do not think you are old enough to buy things on your own.
and...please leave the forum I also suspect that you are not old enough to post anything in this forum.