If you are looking for an interesting way to use an economical bathroom space, a corner toilet might be your best bet.
Corner Toilet Design
Designed with its tank at a right angle, corner toilets comply with government recommendations and building codes, while still taking into consideration your need for high-utility in limited space. A minimum space of 15-inches from the center of the fixture to either side is required. There are even ADA compliant models with raised seating, making them easier for disabled people and senior citizens to use.
Several companies offer corner toilets. While they're a bit more costly than run-of-the-mill models, they are far more affordable than the tankless variety.