Are you planning on buying it online? With body protectors I would reccomend going and trying some on and seeing which one fits best. Its important the back is long enough to protect your lower back, but not so long it catches the saddle, and it should fit around your neck and shoulders comfortably and snuggly. If your after a cheeper price, go in to a shop and try some on before buying online, or ask the shop if they can do a deal with you. Some shops prefere cash payments to card payments due to high bank fees on expensive items.
The charles owen protectors are comfy to ride in, and the zip is good as you don't have to fiddle around with the adjustments every time you get on! I noticed one is adult and one is child size (couldnt get bottom link to work), and this means the sizeing proportions will be different.
For cross country, never compromise on safety unless you have to. Go for the BETA3 standard ones as these should offer more protection.
We lose ourselves in the things we love, we find ourselves there too ~Kristen Martz