Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Lumbar support, Slow rebound, High-quality material
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($45.89): AFfbG10
2. ($45.89): BGBFAFF2019
3. ($45.89): BGCITYADS2019
4. ($47.42): aff7off
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Old coupons (from the oldest to the newest): 502C6B, vipupgrade8, TTxBG10, BGss506, bgssaff9
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for Xiaomi 8H Memory Cotton Lumbar Support Gray is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).