Here are some thoughts.
The 144,000 could be a choir or band selected to learn a song in Heaven, who were the best of the best men and women of God during their time on earth, on another note the size of Heaven is 12,000 furlongs width and length, which is 144,000 furlongs square, so it could mean it's not a literal 144,000 number of people, but it could mean every single person in heaven living within those 144,000 furlongs square.
Revelations 14:3
"3 They sang as it were a new song before the throne, before the four living creatures, and the elders; and no one could learn that song except the hundred and forty-four thousand who were redeemed from the earth."