The W126 was the largest Mercedes sedan made from 1981-1991. Its a big car, even in short wheelbase form, but a long wheelbase model (SEL) is also available, which is a real tank. I have a 300SEL and its a tank, but since its a 6-cylinder, I get fairly good mileage.

Other than occasional headgasket issues, these engines are virtually bulletproof.

If a Camry is too small (I am not sure what generation he thinks is too small, but the 1992-up versions are a little larger), I would also recommend something like a Toyota Avalon (available in 5 or 6 passenger forms), or something like a 1986-90 Mercedes 300E. Same engine as the 300SEL, so watch out for headgasket problems. Its my understanding that if a headgasket issue goes crop up, its not that hard or costly to repair.