Silicone, microplastics, and pumping

I recently switched over to silicone bottles for my baby out of concerns for microplastics etc, as well as wanting longer lasting bottles. I exclusively pump though, and all the bags I use are plastic… I’m just not sure how else to warm frozen milk because I drop off the milk frozen at daycare, and they use warm water to thaw the bags which really doesn’t work well in silicone (aka I don’t think I can freeze them into bricks using silicone molds and then put them in a bag). At home he generally gets fresh milk. I’m just curious if I was stupid to switch bottles because he’s going to be exposed to plastic anyways through the frozen milk bags, or if it was worth it to reduce his exposure?