There currently is one option to travel by night train from Umeå (Sweden) to Stockholm (Sweden), taking between approximately 8 and 9 hours: Namely the 91 operated by SJ.
The Swedish Railway SJ operates night trains daily throughout Sweden, covering long distances and serving remote areas.
SJ night trains offer seats, couchettes, and sleeper cars. The sleeper cars feature various compartment types: for two or three people and single compartments. On some routes, Deluxe compartments with private bathroom and shower are also available.
Each sleeper compartment has a washbasin. The Deluxe option additionally provides a private bathroom with shower.
Couchette compartments accommodate up to six people. Bedding is provided including pillow, pillowcase, sheets and blanket. During the day, middle berths are folded up so lower berths can be used as sofas. You can choose between women-only, men-only, or mixed compartments. SJ offers limited couchette compartments where pets are allowed, and these must be booked as private compartments.