Selection of women's footwear definitely takes a hit above size 13. Amazon.com has a fairly good selection, although most styles aren't very feminine. That being said, selection changes frequently. Zappos.com has a similar selection above 13, but generally more expensive than what you would find on Amazon.
Amazon has a surprising number of crossdressing-relevant items for sale, including clothing, shoes, silicone breasts, supplements, breast enhancement cream, etc. Just search crossdressing in All Departments and have a look around.
For clothing, my guilty pleasure is Forever 21. It's inexpensive (and commensurate quality - not going to last for years), youthful, and they have a large variety. They also have a fairly extensive selection of plus-sized ( = guy-sized in many cases) clothing, including swimwear and activewear. They have a huge selection on their website forever21.com. Be aware, it's here today, gone tomorrow at Forever 21 - many items are available until stock runs out, and that's it. A few items are stocked regularly, but generally the theme is fashion of the month, week, or even day. If you're lucky enough to live near a store (which actually is probably most people, these days), you can check things out in person. I consider the fitting rooms strictly off-limits 😃, but have never been looked at strangely in any way. My biggest gripe with Forever 21 is that there is a low correlation between what is available online and what is in stores. Also, the store-to-store variation in selection is significant, so hit up multiple stores.