Which stocks would you say are well diversified?

So I started investing at the early stages of covid when we all had a bit of extra time. In was researching companies, waiting until the "right" time to invest etc. After a while I realised that I do not have the time to fully research every single stock I put my cash into and it would be too risky to start lumping it into companies without doing sufficient due diligence.

I then looked into ETF's, but quickly abandoned that idea for the usual deemed disposal problems. The only remaining option then was to invest in stocks which they themselves are diversified. For instance, Berkshire Hathaway. The intention would be to invest monthly and avoid the risk of investing in individual stocks in individual industries. My only concern now is that putting it all in Berkshire is a risk in itself and I should diversify more, especially with the impending "exit" of Warren Buffet.

I've looked at alternatives such as JP Morgan and Monks Investment Trust / Scottish Mortgage Trust, but are there any more I should be considering? Obviously I'll be doing my own research into these, but it would be good to get a steer into tickers as a starting point. Thanks!