Look for a headliner material you like. It comes in 72 inch widths which you need to have a minimum of seams.
I just finished redoing the interior of a 13' Bigfoot
I striped the interior down to the insulation and after doing a lot of thinking I had an upholstery shop do the interior.
I like rat fur, but there's no West Coast distributor so I had to buy it from Scamp
There price was competitive with other products but the freight was more than the rat fur.
has a high density foam insulation about 3/8 of an inch thick that I was able leave.
You may want to try to do the same when you remove the ensolite because your going to need some insulation under whatever you use.