This will be our first pool and we are either going with a Sharkline 18x33x54 or something very similar. We had a neighbor once who had a slightly deeper area in his round agp. So I'm wondering if we can put a gradual slope from both ends to the center to a depth of 60" .... and if so, what size liner would be needed? And would it be ok to use foam for the floor? Thank you to all the TFP experts out there helping us newbies!