Since merlin supports LSP protocol, completions, jump-to-definitions and other such stuff should just work in the majority of editors. REPL integration could be a little bit trickier, tho. There should be a mode for editor supporting utop.
There is reasonml plugins for both Idea and VS Code, which provide a good support out-of-the box. However, neither supports repl yet AFAIK. Emacs have a good utop and merlin integration, if you want to give it a try, both Doom-emacs and spacemacs have a preconfigured OCaml support.