Cove molding is a variety of crown molding with a concave profile. I don't find that it makes the ceiling look higher; some experts say that by drawing attention to the ceiling, the ceiling may in fact look lower. To counteract that, paint the ceiling a lighter colour than the walls. Crown molding does make for a smoother transition and is characteristically used in more expensive traditional homes. Or in homes that are aspiring to a traditional look. Plaster Cove Moulding Handpainted Detail on Plaster Moulding Crown mouldings are made of polyurethane and other foams, wood, pre-caster plaster and cast-in place plaster. Here is a link that might be useful: Balmer Architectural Mouldings

An inexpensive way to get a hefty base board is to use 1"x6" boards and a 1 3/8" base cap. It will be nearly 7" tall and it's an easy install. I would use a 1x 3/4" base shoe with that but that's a matter of taste. The base board provides the visual foundation for the room. As such, it's the one piece of molding that can be out sized compared to the rest. Get some of the material you intend to use and lean it against the wall in your room and see if the size works. If you feel that your existing case should be larger a backband is an inexpensive way to add some size. You'll need a table saw for this but if you have one or can get to one it's easy after that. Take some 1"x6" and cut it into strips 1/8" wider than your case is tall. Sand the banding and break the leading edge with sand paper. Install it around the outside of your exisitng casing. When it's finished you'll gain 3/4" in width and extra depth. Visually it will appear even larger. I've never used foam crown but it could work. The trim in commercial buildings is commonly glued on foam. Once it's painted who's to know or care? They used to make it out of plaster even cement and nobody cares. I can't imagine how your crown molding is going to get dented. If you try it report back on how ti went; I'd like to know.

On houzz, New England Colonial search. All these rooms have crown molding. It really depends upon the style of your home overall and if there is crown molding in other rooms. I have crown molding in several rooms in my home, I would call the home style English Cottage. It fits the home style, and feels appropriate.

To me, drywall based molding is cheap. You may not agree and that is perfectly fine. But hear me out. There are some people (like me) that come to your house and think 11 ft ceilings are all fancy but you cheaped out on the details. Now you can dismiss me as a snob and that is fine. But you should know that there are people out there that understand trim and feel like you are being less than genuine. My last hood had 55 houses built by 5 custom builders. One of these areas that was developed and each builder bought lots (presumably 11 each but not sure about that). They then built some spec houses and some custom. All to about the same level (fancy cookie cutter we liked to call it). Trim levels usually pretty ornate. Most with 10 down/9up ceilings. You could always tell which houses were Rudy's houses. Ah the corners he cut..... like drywall based crown. Our good friend's next door bought a Rudy (not the company's name) spec house..... My builder (total trim snob) refers to drywall based trim as a "spec house trick" that he refused to partake in. Better to have no trim than fake trim.... On your other issue - you should post a floor plan. 11ft transitioning down to 9 ft is tricky with door sizes as you are figuring out. But the plan matters. You can mix 8 ft doors and 7 ft doors in the right situation I think.