Backpacking in the Grand Canyon in September

[Laura]

My s/o really, really wanted to see the Grand Canyon after he saw the shots I got in February, so we made plans to backpack there in late September. I thought it was all settled, got the vacation request in, was going to apply for the permit in two weeks....or so I thought. Now s/o is freaking out, thinking it's going to be really hot, really hard, and really miserable (we were planning on doing an easy trail to be determined later). Does anyone have recommendations for an easy trail that a very-in-shape-but-slightly-neurotic middle-aged male and a much more relaxed middle-aged female can do? Also, how hot is the Grand Canyon on average in late September?

Thank you in advance for saving my vacation!