UX research methods for improving the onboarding of SaaS

I am doing research on improving onboarding process of a SaaS product. Can you recommend a methodology and researches for this kind of work?

I plan to do data analysis, heatmaps, video sessions recordings, heuristic evaluation. I plan also doing unmoderated user testing, but I doubt I can do JTBD interviews with a time limits I have.

  1. Is it possible to do JTBD as an online survey?
  2. Can you recommend other low cost/valuable insights researches?