The closest hotel is Quality Hotel Nacka. You can find the hotel on the map. “Dieselverkstaden” indicates where the convention is. You can also use this site for booking! Unfortunately, this hotel appears to be sold out.
ApartDirect Aparthotel Stockholm Hammarby Sjöstad is on walking distance from the convention. Biz Apartment Hammarby Sjöstad is another apartment hotel which is a little bit further away.
Park Inn in Hammarby sjöstad is fairly close to the convention.
Alexandra /Archipelago hostel in Gamla Stan (The Old Town) is situated near buses which rapidly can take you to the convention site. There are several more youth hostels to choose from.