Yes, there is a LOT you can do while pregnant at WDW. I would also say there are a few more restrictions than just the mountains, RnRC, and ToT...
Always, it is good to consult with your doctor shortly before going. If you have any complications at all, then it's not worth risking the baby.
There are a number of rides with warnings posted for pregnant mothers, but perhaps some people use their own judgement on those. I also think even if there's no pysical damage to your body, if you are the type of person who gets emotionally excited or scared, then you should really avoid any type of thrill rides. If you are the kind of person that doesn't get scared on anything, then you might be more adventurous, even if you aren't familiar with WDW.
I think most of the rides with no height restriction should be fine, and there are a number of really great shows at WDW. Some are theater shows, but many are 3-D type shows. They don't technically move, but they are interactive, so they are reallyy 'attractions' not 'shows.' There's the stunt show, numerous parades, daily fireworks in two parks.
You will have enough to keep you busy all day for four days or more. You may not have enough energy to do/go on everything there is to do in four days.
Do plan a few TS meals. You'll appreciate the breaks. DO go swimming, but avoid the whilrpools (unless you just dip your legs).
My sister had a tough time on the safari ride. It looks tame, but it's basically a very bumpy jeep ride, so that can do a number on the muscles under your belly. The same could be said for Star Tours, Primevel whirl, DINOSAUR, Mission: Space, Test Track and maybe Kali River Rapids.
Disney is nothing like Six Flags! Tehre will be lots to do, and even if you want, even when you can't go on many of the rides, you might still be able to, or be interested in enjoying the pre-show with the rest of your family. At the entrance ask about the 'chicken exit.' (A last minute way to exit a ride before getting on the ride vehicle) Some ofthe rides that have a great preshow and a chicken exit include : STar Tours, Expedition EVerest, Space Mountain (You'll get the pre and post-show, though you could also go on the tomorrowland Transit: no line, shows you the area rides, and you get to sit the whole time), and many more. Of course, being six months along, you might also enjoy the opportunity to sit and rest while the family goes on rides too.