That's so nice of you :)
If your friend likes ver sweet stuff, Michalki would be a good choice
you can even get them in some UK Tescos in polish section. Michalki are something that reminds many of their childhood
Another sweets (also available at Tesco) are 'Ptasie Mleczko' (Bird's milk lol)
Polish sweets
It's a marshmallow/cream coated in chocolate