Build window seat without wall studs

So I have a bay window where i want to build a seat into the bay. My house is old (United kingdom built circa 1930) and I can't for the life of me find any wall studs. It's lathe and plaster walls, I've tried a reallybstrong magnet without luck. I pulled out a skirting board (baseboard) under one angled side of the bay window and all that's there is brick. I'm thinking the entire underneath of the bay window is possibly pure brick and mortar. Ive yet to remove the boards under the rest of the window area. it safe for me to drill mount my wooden frames for the window seat straight into brick and mortar?

 

Into brick/mortar absolutely, if you were attempting to attach directly to plaster/lath it might be questionable.

Magnets dont work, what are the odds of finding a nail, get a good, and there are many options, stud finder to locate items behind walls!

 

Several sources online state that stud finders have a hard time locating studs behind old lathe and plaster walls, so I was reluctant to spend the money on one. Also not sure if I was clear, obviously in front of the brick and mortar is lathe and plaster, so I would be mounting the seat frame into lathe and plaster and then brick and mortar behind. Which would mean I would need some crazy long screws for the job then? 2inches of wood frame, plus probably another inch of lathe and plaster until I get to the brick.