And my base layer of choice–when the item in question has not only deep armholes, but also a deep neckline–is a lace longline bralette or a lace-trimmed camisole. The lace fringes add not just additional coverage, but also visual interest. It’s all upsides.
Free People Sweetie Pie Lace Blouson Bodysuit I own this in three colorways, and while that is excessive, buying just one isn’t. The fit is true to size, but the style does run short, so if you are 5’6 or taller, you may need to size up.
Free People Sonny Harem Jogger Pants I own these in black, have been sleeping in them, and have plans to buy another pair; they are so soft. The pants have a relaxed fit (see “harem” in name), so your normal FP size will do. Use code SHOP25 at checkout for an extra $10 off (valid through 09/09/18).
Free People Sydney Bodysuit Runs large (1-2 sizes) with deep armholes, but the sale price is so reasonable ($16.50 in four colors) that I am willing to overlook its issues and still recommend it.
If you need something to add to your cart to push it over the free shipping minimum ($49), I own the Ideology Performance Ankle Leggings and would recommend them; the almost 5-star reviews speak for themselves. And the cropped length is almost perfectly “full” length on 5’2 me.