I can speak to Infinity which is a close sister to Millennium.....The beds are beds, not pull-out berths. If you are traveling without kids, you will have no problem, as you will have the two twins together and it seems like one bed.
The only time it gets close is with a third person and you use the pull-out bed in the sofa. The concierge class cabins are large enough to allow an easy squeeze out to the veranda with the sofa bed out.
If you are in a cabin with a pull-down, they are quite high up and when down are easily gotten under. I have no idea if they have pull-downs on Millenium.
You may want to look into the Celebrity experience versus the Carnival - if you liked Carnival you will find Celebrity quite different. People do dress for dinner, no 'pass the orange' games, night life kinda tails off early....just a different market....if its not your thing you may not enjoy your cruise.
You will not be disappointed in a Millennium class cruise!
north beach nj
major celebrity fan, but
i miss the norway