[Sven7]

I think that heating up the water for the rest of the day when you're not showering is probably more of a waste of hot water than it would be to heat up a new tank full, since it's likely going to heat up a tank full anyway. It'll just take time. Maybe you could take a shower at night and your SO could take one in the morning... that way, even with a low heat setting, you'll both have enough hot water.

Another option would be to get a low-flow shower head and set it on the "eco" setting- it will use less (hot) water. I'm trying to get this done but the end of the L pipe that comes out of the wall won't unscrew.

The expensive solution to the "waiting for hot water game" is a recirculation system. My parents have one and it's awesome. You push a button on the wall, wait a minute, and when you turn on the faucet/shower, hot water comes out. Unfortunately I imagine it would be a money- and time-consuming thing to retrofit.