I spent a couple of nights in Hyeres last summer so I could go out to the Isle de Porquerolles. The island is fine but not fabulous (I'm not a beach person); I enjoyed Hyeres more. It has quite a pretty historic area and isn't overrun with tourists. It's probably at least a 1-1/2 hour drive from Aix, however. And it's not as "different" an experience as you may be seeking. Should you want to visit Porquerolles and do some walking/hiking, wear appropriate footwear or stick to the smoother bike trails. There's a lot of uneven footing on some of the other paths.
Another possibility would be the Gorge du Verdon. I was sorry to miss it, but in May it was not possible by public transportation in a reasonable timeframe. Moustiers-Sainte-Marie, which I think is known for its pottery as well as its location in a scenic area, would be a bit over 1-1/2 hours from Aix.