Definitely depends on your bedroom temperature. Our room temperature is around 20-22 degrees because of the heating - I’m assuming it will stay around that as the weather actually gets warmer. He’s been in a 1 tog bag since he was 1 week.
My room is around 20 its hard to get the heating right as we have electric radiators so its on a time and i dont have it too hot. My daughter is quite a warm baby so she has just a sleep suit and 1tog x
Our room is warm and my little boy runs warms too (20-22) so we have a 1 tog in the tommee tippee bags Most nights it’s been closer to 22 so he sleeps in a long sleeve vest and bag.
We were recommended these merino wool bags which are equivalent to 0.7 to 2.4 togs so you don’t have to keep buying new ones. The also fit them from birth to 2 years. More expensive than standard ones but given you don’t have to keep replacing them it should work out at a similar price in the long run. https://superlovemerino.com/collections/merino-baby-sleeping-bags/products/organic-merino-baby-sleeping-bag?variant=41213294379061
I’ve started using the love to dream 1.5 tog as it’s for temps between (18-22°c)