The best way to check is if his tummy or the back of his neck feel cold, chances are he will feel cold, if they are hot, thenn he will feel hot x
As long as your room temp is between 16-20 degrees celcius you should be ok. The cooler the room, the more layers, the hotter the room, less layers. Our winters can get bad here to the point of -10 so it'll be a vest and a thicker sleepsuit for the wee man. At the moment its 33 degrees celcius here and wee mans room doesn't drop under 27 degrees celcius cause it's too hot so he has been wearing either just a very thn sleepsuit with no vest, or just a vest with a very light blanket over him x
It's during the summer so what worked for me was just put him in a sleeper and when you lay him down cover him with a light blanket. That should keep him from getting to warm but still be warm enough. When you swaddle it tends to get them warmer. That's been my experience anyways. Hope it helped.