The Jags boss is set to lose left-back Aaron Taylor-Sinclair on a Bosman while veteran Lee Mair has been told he won't be offered a new deal with the Premiership side.
Loan stars Lyle Taylor, Chris Erskine, George Moncur and Prince Buaben have returned to their parent clubs.
Thistle will play Premiership football once again next term after finishing 10th on their return to the top flight and Archibald knows he faces a tough task to fill the No.3 jersey.
He said: "I have not put an exact number on it but we will need at least six. The loan players we had have gone back and we have let a couple go so we will need at least six or seven.
"It is going to be very hard to get a good left-back and guys like Aaron are hard to come by, he has been brilliant for us.
"He hardly missed a game, didn't give us any problems and was always willing to learn and take things on board. We will miss him but we certainly wish him all the best.
"With the way we play, with the full-backs high up the pitch and pushing on, it is hard to find someone who ticks every box.
"We have been looking for a while to see who we can bring in but we are not going to panic.
"We don't want to get our fingers burnt and bring someone in for the sake of it."
Having allowed Mair to leave and lost Taylor- Sinclair - who is attracting interest in England -then adding more defensive options to his squad is a must for Archibald in the coming weeks.
Conrad Balatoni finished the season in fine form and while Aaron Muirhead endured an injury-hit final few weeks, Mexican stopper Gabriel Piccolo has proven to be a useful deputy throughout the campaign.
The Jags boss is eager to get as much of his business done as quickly as he can and he has the identikit in mind for the man he wants to fill a centre-back berth.
Archibald said: "It is one area of the pitch that we need to strengthen.
"They are becoming like strikers, centre-backs now, they are hard to come by and are just as important, if not more important, than strikers.
"We searched all January and all last summer for an experienced centre-half.
"We hope that after such a good season this year it will be easier to attract players here.
"Last year we looked everywhere. We brought Gabby in and had a lot of foreign trialists.
"But I would rather have a British-based player and a good talker.
"I would prefer a British-based one to bring on what we have got in the squad here already."
At the other end of the field, Archibald is keen to do deals to bring Taylor and Erskine back to Firhill next term.
But he knows the ball is out of Thistle's court as they wait for Sheffield United and Dundee United to consider the forward pair's fate.
He said: "It is down to their parent clubs. If they become available we will definitely be interested, but it's down to them."