Since you already know SSRS and some T-SQL, SQL Server seems the obvious choice, but I don't know how the market is at your place.

Oracle developers tend to get paid better, but that's probably because they have to work with that sh*tty product 🙂 (just like SAP consultants)

Courses are a way to get up to speed, but your employer needs to sponsor them.

There is plenty of free stuff online though. Go through the forums and sites like Pragmatic Works, PASS Virtual Chapters et cetera to get your hands on free training.

If possible, attend a local SQL user group, if there is any.

Getting certified is also an option. It forces you to look at the fields of SQL Server you haven't worked with yet or haven't got a lot of experience with, so at least it broadens your horizons.

Changing jobs is of course a possibility. If your current employer doesn't support your career goals, you might want to look at for a junior level position somewhere else.