Hmmm, is a straight bar on the same geometry really going to be more comfortable? Your hands are going to be about the same place as they would be if you had your hands on the tops of the drop bar, just wider. And don't forget straight bars only have one hand position, all of them uncomfortable after a long enough time on the bike.

Can you get a higher/longer quill stem and redo the geometry to get a more upright posture? Maybe all you'd need to do is move the saddle forward a bit to go with the higher bar position.

That way you wouldn't have to get all new shifters and/or brake levers.