I have to admit that I have only a passing interest in hibiscus. The modern hybrids (big, thick, colorful petals) that I see in yards around Honolulu are usually grown short, usually no more than 5 ft. in height. I don't know if they will grow to tree height. I also see a variety that is not a modern hybrid, with narrow, thin pink and white petals, growing to about 15 ft. in height. The individual flower may not be much to look at, but it is profuse, so in its entirety it is quite something to behold. But that is only my opinion, as others may see it as only a common pink hibiscus.

I go to a farmer's market where a lady named Jill Coryell sells hibiscus. Known as "The Hibiscus Lady," she has over the years hybridized thousands of varieties. I'm sure she will be able to give you some ideas of varieties that will fit your needs. Her email address is:

hibiscuslady@hawaii.rr.com

I was thinking some more about your question. If you're going to grow a hibiscus tree, it might be better to select a variety where the flowers "look down," or have a droopy look. Most of the modern hybrids "look up," so if they grow into a tree and you view them from below, all you will see are the undersides of the flowers. If I remember correctly, there's an old variety called "Japanese Lantern" or "Chinese Lantern" that looks down. It's red and has frilly petals.