A goalless draw at Hereford on Saturday, together with Macclesfield's defeat at Bradford, means the Cobblers hold an unassailable eight-point advantage over the bottom two clubs with just two games remaining.
Boothroyd, who succeeded Gary Johnson at the end of November, said: "We have survived and that was the brief when I took the job, to make sure we stayed in the league.
"Now it is about building. The players are off (on Monday) but I am in the office and I will be speaking to one or two people and perhaps getting them down to the ground. I will also be speaking to the ones I want to keep and ones that I want to let move on to pastures new and I can start making those decisions now.
"I have managed to speak to a couple of people very early and have put the feelers out, all legally and above board of course, and now it is a case of showing them around the club.
"I would like to go into pre-season with a group of players that are going to be the core of what we do next season."