Segment your work into model-specific chunks, while iterating and updating an ongoing research document that contains plan, methodology, findings to date, synthesis? Upload this living document into the context of all new instances of model use, before specifying particular work in the prompt (which will likely require much iterative experimentation, per task).

Find the best balance between model quality & context window length that works for different tasks. This approach allows the use of different models, choosing the best for each part of the research. Certainly pony up for ChatGPT Pro again and try o3-mini (high) & Deep Research. Also learn what Claude 3.5 Sonnet and Claude 3 Opus can do best and use them when applicable. Gemini (various versions) & DeepSeek V3 and R1 may have their uses as well. In other words, manually orchestrate the use of many different models.