ALL the other stations including Hua Lamphong and Bang Sue have both platforms on the same level.
Have used the MRT quite often, and have certainly passed through all the stations, and used quite a few to embark or disembark. Most often Sukumvit because it's close to my place, but also stations like Lumphini, Silom, Hualamphong, Bang Sue, Chatuchak Park, Lat Phrao, Huai Kwang, Rama IX and Phetburi.
Sam Yam I have never used since the only thing of interest there (Wat Hualamphong) can be easily reached from silom.