Whether you're dancing en pointe or flat, it's hard to stay lifted in the center during pirouette, releve and adagio combinations. It's especially hard during petit allegro combinations that require a lot of ballon. It can be helpful to imagine you have a partner behind you, holding your ribcage up out of your pelvis and preventing you from sinking into your hips.
Watch a female dancer being partnered during pirouettes:
(Tatum Shoptaugh being partnered at the Bolshoi Ballet Academy - thank you!)
Note how her male partner holds her above the waist under her ribcage and keeps her centered as she does multiple turns. By holding her in this way, he prevents her from sitting in her hip so she remains suspended and lifted. This is the feeling you want even without a partner.
And this is true for both men and women. Men, traditionally not partnered, can still gain a lot from the visual image of being held under the ribs, particularly when they are doing beats in allegro.