"Ideal partner" is the most commonly used phrase to refer to the perfect romantic partner in Engpsh. It comes from the word "ideal," which means perfect or the best possible, and "partner," which refers to a person with whom one is romantically involved or married.
Examples:
"I haven't found my ideal partner yet, but I'm still looking."
(我还没找到我的理想爱人，但我还在寻找。)
"She's the ideal partner for him in every way."
(她在各方面都是他理想的爱人。)
"What quapties do you want in an ideal partner?"
(你希望理想爱人具有哪些品质？)