Comfy on the bottom, chair for sunbathing topless is comparatively new (7)
I believe the answer is:
younger
'is comparatively new' is the definition.
('young' is associated in meaning with 'new')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for younger that I've seen before include "Not so old" , "Seven PM" , "Less experienced" , "more boyish" , "Less mature" .)