Hello. Traditional queen innerspring mattresses have a problem with two adults rolling together. Eastern King not so important. Check the warranty failure bin, if they are going to have a problem it is with high centering. Guess most couples sleep in the exact same position on their side.

Pocketed coils are better. Personally I prefer four packs to the simmons/southerland absolute individual style but four packs are a bit more difficult to find.

How tall are you? The size you probably want if you do go for two mattresses is twinXL. Pick a mattress with a good border system you CAN NOT FEEL and I bet it is 90% as good as a single mattress if you do decide to cross over the middle of your bed ever.

I agree with Toronado eventually two adults are going to end up rolling together with an innerspring mattress. I also agree that pocketed coils are a better option. Personally I think Tempurpedic with all the options they have now is one of the safest ways to go, although it is an expensive one.