The house we recently purchased has a 1 year old gas hot water heater
that appears to be undersized for the house.

The house has 5-6 bedrooms and we are a family of 6, yet the tank is
only 50 gallons. We typically run out of hot water after 1-2 baths and
a couple of showers.

Seems to me we have a couple of choices:
1. Take fewer, shorter, and more spaced out baths and showers
(not acceptable per my wife and kids

2. Replace with new larger tank (100 gallons?)
(however, existing unit is almost new, so this sounds a bit
wasteful)

3. Get a second hot water heater
(Can this be done? Can you just get another storage tank or do you
need 2 separate full heaters? Are they connected in series or parallel?)

4. Get some type of booster such as an auxilliary tankless heater?
(Is there some type of booster that only comes on when the main
tank is depleted and that would not be too costly to purchase or
install?)

Assuming that #1 is not an option (at least per my wife), what
approach would you recommend?