I have fitted UV film to my windows and it's not that difficult. With the kind I bought you use diluted Johnson's Baby shampoo (seriously!) as a slip solution to help slide and adjust the film into position. It's easily available on eBay (the film and the shampoo ;-)), however I'm paranoid about UV damage because I know just how harmful it can be, so I also keep the curtains closed too since even low levels of UV will damage non light-fast inks over time, which means your cards and boxes WILL fade eventually if exposed.
It makes me weep when I see fantastic collections displayed anywhere near sunlight. I absolutely do NOT trust them simply being out of direct sunlight, as UV can and does reflect just like visible light (and if you stop and think about it, why wouldn't it?). You are able to see into the corners of your room which don't receive direct sunlight because they receive reflected visible light, but they also receive some reflected UV. It's at a much, much lower intensity obviously, but that's not the same as receiving zero UV.
Here's an article about surfaces that reflect UV. It's talking about outdoor surfaces like paint reflecting UV, but the same principle still applies to that amount of UV light that your window glass fails to absorb: https://www.uvdaily.com.au/blog/reflected-uv/
