Perhaps it would be easiest to just use more than one RE. Another easy way is to check that it doesn't match what you don't want:

$input !~ /\d|\pP|\s.*?\s/;
[download]

(Not sure if you mean more than one consecutive space or just more than one space; or if you mean whitespace characters or just the space character; adjust to suit.)

I see in a followup that you perhaps mean any non-word non-space character when you say punctuation. So maybe something like: /[^\w\s]|\d|\s{2}/ (which will still allow _; if you don't want that, say /[^\w\s]|[\d_]|\s{2}/).