I would exit the airside of Changi, and do something interesting. As mentioned, there is now a Yotel location in the new Jewel (shopping and eating). Jewel is quite lovely.
And, unless you are already overly familiar with Singapore, you could go into the city for your 22h layover on the return side. Again: Yotel on Orchard Road (near Shaw House) is very nice, good price, and good location.