To help keep your baby stay asleep during cooler night's when the temperature drops, we suggest the following options;
1. We designed the the ergoPouch Arm Warmers for this exact reason. It's a cute and simple cardigan-like design that can easily be worn over any of our sleeping bags (including swaddles), giving your child an extra tog layer if required. The Arm Warmers are great for all-year round, particularly for Autumn & Spring
Made from organic cotton stretch jersey and features organic cotton fleece sleeves with fold down mitts.
Sizing available in 2-12 and 12-36 months
Available in White (Natural)

2. The 1.0 TOG Long Sleeve Layer is a great item to wear around the house before and after bed, keeping your child warmer than most onesies on the market (which are usually 0.2 TOG).
If you already have a 2.5 TOG bag and don't wish to purchase a 3.5 TOG (the thickest) bag, then we recommend this 1.0 TOG Long Sleeve Layer (PJ's) to add an extra TOG for warmth.
Available from newborn until 3 years old (we suggest going a size up from 1 year).

3. Another option is to unzip your sleeping bag from the bottom up when putting your child to bed when it's a little warmer for more air flow, then zip closed later in night when it's cooler.