Since you're open to used, I'd look into something on this level
Manley Chinook tube phono preamp For Sale - US Audio Mart
tubed, good reviews. I demoed one in my setup. These can be had for less, if you're a negotiator or patient/ready to pounce on better price.
The Mani is great for what it is-a $150 phono amp. I had one as a backup while getting my proper unit repaired.
"I am using a Willsenton R8 integrated Chinese-made tube amp with KT88 tubes "
The PL will have noticeably better construction details/parts, but It may not be leagues "better" in SQ?
Based on things I've read, it's a decent amp-for the price. Just how much "better" the PL integrated would be something between you and your ears?
That's where separates AND your wallet will make a significant difference.
The bad news you should already know is it always adds up to the sum of ALL the parts.