Sleeping arrangements at MIL

So my boy is at his Nans one day a week, with daily naps, and sometimes sleeps over on the odd occasion. I feel like he is slowly growing out of the travel cot she uses. What would be the next step? He’s still in a cot a home with sides. Do I get a bigger travel cot for hers for the meantime untill he’s in a bed, and then just get a bed guard or something so she can attach to a single bed