A 19 month old is really too young for a sit and stand type stroller. There isn't a real seat for her and there isn't a harness to hold her in. When they are older it may work for you...but not as a first/only stroller type situation.
Have you tried out a Phil and Ted's Sport yet? I know you said you didn't like the idea of one child blocking the other - but most feel that way until they try it out! There are lots of configurations and your older daughter would be in the top/front seat most of the time. The side by side ones are BIG. Since your DD is so young - you will have a lot of time in strollers and will find the side by side ones cumbersome when you go into a store, go to a crowded festival, etc.
Try the Phil and Ted's before you decide :)
Good luck!