If you need a really unique and special engagement ring, forget the diamond. Even when you have a normal weight, if your parents have fat fingers, you might be most likely going to have one if you don't have one already. A couple would wear an engagement ring each during their engagement. Go for gems that are rarer than diamonds.
DivaDiamonds 14K White Gold 3 Stone Channel Set Round Diamond Engagement Ring (1/4 cttw, F-G, VS) - Size 6Amazon Price: $800. During the wedding, the three rings are joined together to become one. Their lighter colored counterparts are referred to as green beryl. Most jewelers offer at least a small choice of pear cut diamond engagement rings.
Three Stone or Other Intricate Design. That has evolved, of course. If you're expecting a princess cut having a single stone, they usually are not the designers for you. If you might be nearby the area or can fly to Ny to meet him, do it.