Changing a roost after 7 and 1/2 years

For 7 and 1/2 years, I've had the same chickens. Well......7 of the 17 are still around. I've had a ladder roost.....about 8' long and 4 and 1/2' tall, with several horizontal 2x4's leading up to the highest roost.
The girls love it because the top roost lets them look out of the window, and also roost on the window sill. They love it in good weather.
But......they are getting old and I think they are getting hurt getting up and down. I need to lower it all quite a bit. Will this confuse/depress them, if they can't get up to the window? Would it be okay to just put a couple cement blocks on each end, on the floor, with a board on top of it? Should it be a 2x4 piece of wood, or something wider so they can actually rest their entire bodies on it (like a 2x6 board)?
I want them to be happy in their old age....but I don't want them to die by falling off the taller roost.
Thanks for your suggestions!

 

Thanks everyone,
The problem I'm having, since they are older, is that they are having a bit of problem getting up and down........especially down, and sometimes they run into the other side of the coop/the feeder, etc. Maybe I'm too worried about their emotional state of losing looking out the window.
Even when they were very young, I think I lost 2 from falling from the roost, or hitting an immovable object while jumping down, or fighting with each other over who gets to sleep where and they got knocked off!
Is there any disadvantage to having a roost too low? Does it go against their instincts?
Even though there are several lower 2x4's for them to roost on, they always go to the top one. And there's 2-3 of them who try to sleep on the narrow window sill, that's even higher than the top roost.
I was thinking what I could do is remove all the top rungs and just leave a couple at the bottom. But then they would be about 4-5' out from the wall. Would that bother them?

They're old and have been such good feathered friends to me..........I want them to be happy and comfy!