Tree I introduced a dummy at 5 months which transformed sleep for us. He has it at sleep times but I try to limit it in the daytime unless he's really grizzly and whingy.
At 5 months he was having three naps and a 6.15pm bed. He was waking once for feeds at night but the dummy really helped for any other wake ups especially with the early 5 am wake ups. I used to pop him on his side with his arm cuddling a teddy, put his dummy in and stroke his head a few times and shush him then quickly leave the room. He would generally go back to sleep for an hour or so.
Once he hit 6 or 7 months he dropped that third nap and he went onto the 2,3,4 schedule and he started weaning. It's then that sleep really improved for a while and naps got longer.
However sleep as per my last post has gone pretty bad. Taking 45 mins to settle for naps, standing up as soon as I lie him down and crying holding onto the bars, only cat napping 30 mins, refusing to go to bed, messing with his bedtime milk, trying to push it away and biting the teat and not drinking, then taking ages to settle and waking up at 9.30pm. I don't know what I'd do without his dummy. I know I have to wean him off it at some point but if he didn't have it he'd just scream the house down....and he has a very loud voice!