I can recommend govim, it's using LSP behind the scenes. I'd also recommend tagbar because it uses the newer ctags fork which supports much more languages.

[1] https://github.com/govim/govim

[2] https://github.com/preservim/tagbar

Thanks. I'll have a more thorough look tomorrow. I'm glad to see that neither seem to depend on NeoVim, which is also something I haven't bothered to take up.

Neovim is great. I highly recommend switching.

I have https://github.com/prabirshrestha/vim-lsp in my minimal config and pretty much the default configuration for it. I only use LSPs for completion, auto imports, rename, and goto definition (less useful when the project is small) and that has been enough for me.