How do you diversify style when playing piano?

Typically, it's hard to sing and play at the same time, initially at least, if the piece become too complex. When improvising/playing by ear, I want to try to create a different sound with each song. Is this possible using only the piano, or is a keyboard necessary to do this? I switch up chords, but what else can I do in terms of style? In other words, how can I enrich my backdrop sound (emulating a professional level) when singing? I haven't played much with any sophisticated keyboard or sound devices. Thanks.