Cos lettuce - drooping

I've been growing these on the windowsill in my conservatory and they seem to be flourishing but a little top heavy. It wont be long before they simply droop over the side of the pots. My first instinct is to put some canes in there and train them but I'm worried that will damage the root systems. Any advice?

 

I suspect it is too hot in your conservatory. Lettuce is a "cool season" crop, and does better in Spring and Autumn than Summer - and I guess your conservatory is more like Summer?

Make sure they have plenty of water