Cruising... roll on roll off?

Am off to Egypt this weekend and have nothing booked. I like the flexible approach and have a reaosnably flexible budget...
Will probably arrive in Aswan early next week and look for a boat up the Nile to Luxor.
Am not too keen on the camping/no toilet style felucca but if I choose one of the floating hotel style cruise boats would like to have a look round some before I choose.
Ideally some kind of mix and match would be great. (One day on a feluca, the rest on a nice (semi-)luxurious boat.)
How easy is it just to rock up in the morning from the overnight train and be on a decent boat heading down the Nile the same day or the next day at the latest?
Do I just head to the river and will be spoilt for choice or am I going to have to do a day of scouring??? Thanks in advance.