Ps. He just turned 4 months
Sleep training is difficult,imo one of the hardest parts of parenting.
My son co- slept with me so there was no holding or fussing. You could also have someone else try to put the baby to bed for you if you are doing the cry-it-out method then you get hold baby to sleep and put him in the crib and every night just keep putting him in the bed while he's a little bit more awake each time that way eventually he's awake when you put him down the crib and you're not holding him to sleep anymore it just depends how you want to go about it