The handlebars and stem assembled on the bikes are by default the only ones we provide.
The geometry and components of the bikes are designed and chosen to provide the most ergonomic position for each bike model and respective frame size, where the load of the entire body is evenly balanced, thus providing the most optimal riding position. Mounting a steeper stem or a higher handlebar will not automatically lead to more comfort but instead to a less agile and thus shakier steering behaviour.
If you are considering our Curt model, but want a higher seating position, more comfort and more features, take a look at our Stout and Stellar models instead. We also recommend a longer test ride on the right frame size for you to get a reliable impression of the model.