Depending on the construction of the reboiler, the steam does not have to be at the same pressure as the reboiler. So you can just pick any pressure. Of course the steam must be somewhat warmer than the reboiler.
Steam is generally available at one of three pressures: Low, medium, or high. Exactly what pressures those correspond to depends on the facility. Consult a design book such as Towler and Sinnott (
https://www.sciencedirect.com/book/9780 ... ing-design) for detailed guidance.