Dressing baby for nighttime

I’m a FTM and worry about dressing our newborn appropriately for sleep. He was a preemie born at 36w4d. He is now 12 days old and surpassed his birth weight now weighing 5 lb 8 oz so he’s a little guy. The weather is changing in northeast PA and it’s getting into the 40s at night now. Our room temp is usually 68-69F at night. We had been dressing our son in a long sleeve onesie and halo sleep sack at night but lately he has been fussy and waking a lot and I am afraid he may be too cold. Based on my temps, does he need more? I am terrified of overheating but also want him comfortable to sleep soundly through the night. I am such a worrier and constantly reading about SIDs isn’t helping.