There currently are a variety of options to travel by night train from Stockholm (Sweden) to Luleå (Sweden), taking between approximately 12 and 16 hours: Namely the 92 and the 94. These lines are operated by SJ.
The Swedish Railway SJ operates night trains daily throughout Sweden, covering long distances and serving remote areas.
The night trains include seating cars, couchettes, and sleepers. The sleeper cars provide compartments for two or three people as well as single compartments. Some routes also offer Deluxe compartments with private bathroom facilities and shower.
All sleeper compartments at SJ are equipped with a washbasin. The Deluxe compartments additionally offer 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.