The former Doncaster boss told BBC Radio Bristol: "Ideally I'd like to bring in a striker, a centre midfielder and right winger.
"We've already got four players on loan so we've got to look for permanent deals really."
He added: "We're trying to make sure we get the right deal and not just anyone."
Penney, who brought in defenders Cian Bolger and David McCracken on loan from Leicester City and Brentford respectively last week, wants to extend McCracken's deal until the end of the season.
The Pirates are currently 21st in League One, two points away from safety.
Source: BBC Sport