I am going on the Rick Steves tour in May 2016. I am coming in a day early, but I just found out there is a big convention in town and just about everything is booked, including the first hotel on the tour. Does anyone know of a place that might work? Thanks!
I would try Airbnb; there are bound to be many places available.
Look at the Scandic Hotels website as they have seceral hotels in Stockholm. We enjoyed the Scandic Hotel Hasselbacken on Djurgarden
I use hotels.com. I've stayed twice at Hotel Hornsgatan on Sodermalm in Stockholm. I loved it. Some rooms have the bathroom down the hall, as did mine, but it was not an issue as each bathroom is a single and VERY clean bathroom. This is a small hotel (21 rooms) with extremely helpful and pleasant staff. This is not the type of hotel that fills up from conventions, IMO. Easy and scenic walk to Gamla Stan. I stayed here on my first completely solo international trip and felt wonderfully safe.
Send an email to the first hotel on the tour and ask them where you should book. Ask specifically if they can help arrange a good alternative for you that will be convenient for moving over to their place on the day the tour starts. That way it will ideally be just a quick walk with your bags to move to your new room.