Perform a non-regex search/replace in vim
For the :s command there is a shortcut to disable or force magic. To turn off magic use :sno like:
:sno/search_string/replace_string/g
Found here: http://vim.wikia.com/wiki/Simplifying_regular_expressions_using_magic_and_no-magic
Use this option:
set nomagic
See :help /magic
The problem is primarily caused by confusion about the role of the & in the replacement string. The replacement string is not a reg-ex, although it has some special characters, like &. You can read about role of & in replacement string here: :h sub-replace-special .
I suspect the main problem for OP is not necessarily typing the extra backslashes, but rather remembering when a backslash is needed and when not. One workaround may be to start making use of "replacement expressions" when unsure. ( See :h sub-replace-expression.) This requires putting a `\=' in replacement string but for some people it may give you more natural control over what's being substituted, since putting a string literal in single quotes will give you the replacement string you want. For example, this substitute does what OP wants:
:s/</\='<'/g
If you want to search literally, you can use the \V regex atom. This almost does what you want, except that you also need to escape the backslash. You could define your own search command, that would search literally. Something like this:
:com! -nargs=1 Search :let @/='\V'.escape(<q-args>, '\/')| normal! n
And then use :Search /foobar/baz
For Substitute, you could then after a :Search command simply use
:%s//replace/g
since then Vim would implicitly pick up the last search item and use the for replacing.
(Just want to give you some ideas)