Ships for Space Travel

I lay watching Mars the other night, and I thought about how we might
build a ship to take people there. In a lot of ways, we are like
ancient man right after he has built his first boat, yet we are trying
to cross oceans in our flimsy craft.

It seems to me that we need something with a lot of volume for long
distances. It doesn't need a lot of mass, maybe something like a big
bubble.

The pressure hull need not be terribly strong, but it should be
protected from impacts inside or outside the vehicle. Of course, the
docking ports would need to be stronger, and so there would probably
be some sort of skeleton that is much stronger than the pressure hull.

I like the plan to have a perpetually cycling ferry running between
Earth and Mars. It could be a simple craft. Maybe we could beam power
to it, perhaps by laser to solar panels? Then, we would could have
simpler, lighter and safer power for the astronauts (the only
realistic alternative would be nuclear reactor, which is fine for
unmanned craft, but not so great for manned). The engines could be ion
engines, using an inert gas, so there would be less risk of explosion
or poisoning by the fuel.

What other sorts of things might differ between this interplanetary
ship and the vehicles we currently have?