It’s much easier to regain earned fitness than to get to new fitness levels. Since you already started SSB I suggest you double up on it to cristalize your base. One of the reasons I suggested TB first are the drills. There are a lot of drills in SSB but they are done at a much higher power requirement. And since they add quite a bit to the perceived workload learning the at low power requirements seems the way to go.
Best of luck to you!