Absolutely some plant matter will help ease some stress off the fish - it sounds like the Betta you received before was probably a bit too delicate. It happens, and I don't think it was your fault that he died.
It's common for fish to arrive with faded and pale coloration - so don't panic if you see that. However, so long as you are taking all the necessary steps, you're doing all that you can do. Sometimes, a fish just won't make it no matter what you do.