Does anyone have experience with Glerups sizing and break in?

I bought some Glerups slip-ons after seeing them recommended everywhere. I really like them, but the problem is my true to size UK 5.5 feels a bit too loose and my toes are hitting the end of the next size down (UK 4.5) when I walk so I imagine that would eventually bust a hole in the end. Unfortunately they don't do half sizes. Customer support said they do stretch over time (I'm not sure if they do in length though?) and if I didn't want to risk making a hole in the smaller size an insole might help the larger size fit better. Which option should I go for?