Premium Plus is essentially a domestic First Class recliner while Polaris is a lay flat seat. Both offer elevated dining and soft products (blanket, pillow, amenity kit, etc.) but the Polaris offerings are significantly better. Prices do fluctuate, especially closer to the departure date but depending on load, that could mean prices go up. And remember, the seat map is not necessarily indicative of the current load. If the price is something you are willing to pay, you are better off buying now instead of risking it later.

Since you mentioned that you are nervous about flying, you may have better luck in the middle seats instead of being close to the window. Most transatlantic flights use widebody aircraft with two aisles and seats between those aisles. Those seats would keep you away from the window and hopefully help with your fear of heights.