It looks like you have two separate questions there:
- How much wiggle room do pool table covers have based on size advertised? How tight should a pool table cover be (or not be)?
- What type of materials should I consider when buying a pool table cover?
I will break my answer into two parts accordingly.
Pool Table Cover Size:
That's weird, you must have a pool table with wider rails or a more bulky apron design. Most 7-foot pool tables would measure in at a standard 89.8" X 50.2", but you are a good 2 inches larger on each axis.
Usually there is a little "play" or leeway in pool table cover sizes, but almost 2 inches - I am not 100% sure. Going larger isn't really a problem except it might not look as "clean" as you might want. Then again, you may not care about that at all.
I know I wouldn't want the extra hassle of having to shimmy on a pool table cover that is slightly too small. After a while I would end up just not using it. If you look at reviews and questions for any pool table cover on amazon (links at the bottom of my reply) you will see some complaints and question/answers where the folks said they can be tough to get on especially around the corners.
I guess if you are buying locally, you usually would have the option to return a cover that doesn't fit. You'd have that option online as well, but it can be a pain in the ass having to ship a package back, wait for refund, etc.
Pool Table Cover Materials:
In terms of material, you'll get what you pay for. The material you choose should be based on your needs around the following considerations for a pool table cover:
- What will look good in your room. If you have a high-end room full of expensive furniture, a cheap plastic pool table cover will look like garbage.
- All covers will protect against dust, pet hair, etc. Doesn't matter the material.
- Decide if you need it to protect from liquid spills. If yes, then make sure you check the material it is made from to see if it repels liquids and/or is completely water-proof.
- As mentioned in this article on what to look for in pool table covers:
Most pool table covers, however, are not thick or heavy enough to protect the billiard table from anything pointy or sharp like dog or cat claws. I know it sounds funny, but cats especially love to perch up on higher areas, so a pool table is prime lookout points for cats. If you have one, you may want to upgrade your pool table cover to a heavier one.
Price and what you can afford.
Leather would probably be the best if you need absolute protection against such perils. Some of the heavier materials will also have a soft cotton backing to ensure the pool table cloth isn't damaged in any way by the heavier material.
Here are a few of the most popular heavier-duty covers (links to amazon.com):
Let us know what you eventually decide, and how it fits!