You can set foldnestmax=1
temporarily, move to next fold and set the option back to its original value:
:nnoremap <silent> zj :let max = &fdn<bar>let &fdn = 1<CR>zj:let &fdn=max<CR> :nnoremap <silent> zk :let max = &fdn<bar>let &fdn = 1<CR>zk:let &fdn=max<CR>