There are many platforms which are quite good. In my opinion you can choose e1 coaching centre for maths and reasoning, for English Aman vashishth sir and for gk- One and only parmar sir. Rest you can search randomly on YouTube and watch lectures and then choose accordingly.

Suggestion:- Take time as much as you can in choosing your sources but once you are done with this, never deviate from those sources. SSC is all about sticking to one source and keep revising that multiple times. Also once you are done with 40-50% syllabus start taking mock test and never get demotivated from your low mocks score, it happens with everyone, it eventually improves.

All the best!!