Bathtub despite small storage?

Hello, we have bought a house and want to renovate the bathroom, we would like to install a bathtub. It should be a corner bathtub with the dimensions 1.40m x 1.40m with 290l water volume. However, we have the heating in the attic with a wall-mounted storage tank from Vaillant (vih cb 70) with 63l hot water storage! That will definitely be too small, what options are there now? Smaller bathtub?

I am grateful for tips and solution suggestions!

Cold bathing would also be possible.

It is clear that a new concept for [Warmwasser] is needed.

Instantaneous water heater would be my first thought.

We once had a 70L hot water tank, which was just enough to heat a small standard bathtub (about 200 liters). If the dishes had been washed in the kitchen beforehand, you would sit in a puddle, then the water would already be cold...

During the bathroom renovation, we chose the Kaldewei Studio Star bathtub for space reasons, higher than others, egg-shaped, and very economical with about 150 liters. Expensive, though. We could bathe hot in it. I therefore do not recommend a large lounge bathtub where the water cools down again before you get in.

Simply just a different heating system / larger storage tank.