In answer to a recent request, I checked with my local Yoga "maven" and got this reply.
"The best place for Yoga near the convention center is the Fitness Center at the Harbor Court Hotel (550 Light St). The drop-in fee is $5 for Yoga class only. (to use the full fitness center the charge is $10 and includes the Yoga class).
Sat 10th 8-9 a.m.
Monday 12th 6-7 a.m.
Tues 13th 7-8 a.m. and 6-7 p.m.
Wed 14th 6:30-7:30 a.m. and 6:30-7:30 p.m.
Thurs 15th 7-8 a.m. and 6:30-7:30 p.m.
The Fitness Center is located on the 7th floor and there are lockers available.
There are also Yoga classes at the HarborView condos' fitness center. That would be a taxi ride away. The address is 100 Harbor View Drive, 410-752-3488.