The Gunners moved back to the top of the table as they came from behind to win 3-1 at West Ham, where midfielder Aaron Ramsey limped off with a thigh strain which will see the Wales international miss the remaining festive fixtures.
There is little respite for Arsene Wenger's squad as they head to Newcastle on Sunday.
German international Mertesacker feels being able to call on the likes of compatriot Lukas Podolski - who scored in what was a first appearance since August - again can prove a big asset in the coming weeks, with England midfielder Alex Oxlade-Chamberlain also closing in on first-team contention to boost Wenger's options.
"We need the right additions. We said that a lot in the summer then Mesut Ozil came, but at this time, in a very special period that only happens in England, you need to get the right additions with players who come back from injury," Mertesacker told Arsenal Player.
"We lost Aaron Ramsey [against West Ham] so a good player is maybe out for two or three weeks, so we need the right additions now.
"We have a good squad and that is going to be vital in the next couple of weeks."
For a while it looked like Arsenal might be haunted by a string of missed chances at Upton Park, where Carlton Cole put the Irons ahead at the start of the second half following a handling error from goalkeeper Wojciech Szczesny.
However, Arsenal's pressure eventually told as Theo Walcott's double turned the match around before Podolski's sweet left-foot strike made sure of victory.
Mertesacker felt the squad showed great character to come through what was a testing encounter against Sam Allardyce's relegation battlers.
"During the game we always believed in our strengths," the German international added.
"We want to go on another good run so at the minute we are really proud we are really proud that we came back against West Ham and it shows our character."
Wenger hopes Podolski's return can prove a big asset.
"I try to get him slowly back to competitiveness and he has shown that he can have a huge impact because he can score and make you score goals, give assists," the Arsenal boss said.
Arsenal - who had not won for three Premier League matches to lose their five-point lead at the top of the table - now travel to the north east for what is set to be another testing fixture of the hectic festive season.
"It has been a difficult period but mainly down to our schedule," said Wenger. "I completely think our schedule has been absolutely horrendous."
Arsenal will have midfielder Jack Wilshere back from a two-match suspension at St James' Park, while centre-back Laurent Koscielny is hopeful of recovering from a gashed knee.
Captain Thomas Vermaelen has performed admirably alongside Mertesacker on his return to the team.
The 28-year-old Belgium international, whose current deal runs out in June 2015, has been linked with a January move away from the Emirates Stadium to secure regular football in World Cup year.
Vermaelen, though, maintains he is only focused on helping achieve Arsenal's collective ambitions.
"I don't like to talk about my situation. It doesn't matter," Vermaelen told Belgian TV station Sporting Telenet.
"I am a player of Arsenal and I will do everything for this club.
"We will see what happens. It makes no sense to speculate about my future.
"We are still happy about our place in the table, to be title contenders we have to be very consistent.
"In the Premier League, everything is possible."