I would recommend an 89 300E (gas) ( I have owned a 1990 300E - 3.0L gas version since 2000 - currently 172K miles) but advise caution on your expectations. It is after all a twenty year old car (even with low mileage).
First expect to repair the head gasket eventually as it is a weak spot on these car.

A great thing about a 300E in this era (prior to '94) is that they share so much mechanically with the 190 series. I see plenty of gas 190s in the junkyard when searching for parts which means I can almost always find what I want. Although there are some '80-vintage 500 series there too, it is really easy to get parts for the 300 series

My 1990 is great fun to drive and is still tight riding down the rode. It is a tank. I can understand you not wanting to buy diesel fuel. The price of diesel is outrageous (even with the better mileage).
If you do get a gasoline 300, DON'T run in on anything but premium or it will destroy itself.