Earth or BhuMandal (भूमंडल) seems to be fit in this context rather than entire universe:
- Similar verses are there in Devi Bhagvatam: Skandha 8: Chapter 21 too:
मूर्धन्यर्पितमणुवत्सहस्रमूर्ध्नो
भूगोलं सगिरिसरित्समुद्रसत्त्वम् ।
आनन्त्यादनमितविक्रमस्य भूम्नः
को वीर्याण्यधिगणयेत्सहस्रजिह्वः ॥ ५ ॥
एवंप्रभावो भगवाननन्तो
दुरन्तवीर्योरुगुणानुभावः ।
मूले रसायाः स्थित आत्मतन्त्रो
यो लीलया क्ष्मां स्थितये बिभर्ति ॥ ६ ॥
He is upholding the earth with the mountains, oceans, rivers and all the beings as if an atom on his thousand heads. He is infinite. His power knows no decrease in any time. No one can describe his actions even if one had thousand tongues to speak.
He is of an infinite strength, of the endless high qualities and of unlimited understanding. Thus staying at the bottom of the earth, the Bhagavân Ananta Deva is upholding with ease this earth for her protection, unaided and independent. ~English translation from sacred-texts
- As explained here, Prabhupäda himself explained the term Bhügola as below:
Bhügola, the earth is round
Bhü-gola. Bhü means the earth; gola means round.
- Dictionary meaning of Bhügola from spokensanskrit :
earth or earth-ball or terrestrial globe or planet earth
- Other Translation for 5.25.12-13
After adding 5.25.13 (to have more context), below is the traslation by vedabase (refered in the Question)
SB 5.25.12 — Because the Lord is unlimited, no one can estimate His power. This entire universe, filled with its many great mountains, rivers, oceans, trees and living entities, is resting just like an atom on one of His many thousands of hoods. Is there anyone, even with thousands of tongues, who can describe His glories?
SB 5.25.13 — There is no end to the great and glorious qualities of that powerful Lord Anantadeva. Indeed, His prowess is unlimited. Though self-sufficient, He Himself is the support of everything. He resides beneath the lower planetary systems and easily sustains the entire universe.
And this is how these verses are traslated by others:
By Gita Press
Who can (hope to) exhaust by counting, even if endowed
with a thousand tongues, the (list of) exploits of that infinite Lord, whose prowess cannot at
all be measured because of its unlimited nature, and on whose (one) head has been placed
(by Him of His own free will) the terrestrial globe—with (all its) mountains, rivers, oceans and
(numberless) living beings like a (mere) atom, while He is possessed of a thousand (such)
heads? (12)
Such is the glory of Lord Ananta, possessed of infinite strength and numberless
virtues and potencies, who supports the earth (on one of His heads) as a (mere) sport
(without any effort) for the maintenance of the entire creation, residing below the earth.
Himself supported by ( none but) His own Self." (13)
By Motilal
On one of the heads of the thousand-headed Lord
lies like an atom, the terrestrial globe with all its mountains,
rivers, seas and the living beings (inhabiting it) , owing to the
infiniteness of the immeasurable and innumerable exploits of
the Almighty Lord, who can, even if endowed with a thousand
tongues, hope to count completely all his herioc acts ?
Of such prowess is the glorious Lord Ananta. His
energy and excellent attributes and potencies are limitless.
Unsupported by anyone else, he stays at the bottom of the
earth bearing it easily for the preservation and wellbeing of
the entire creation.
Footnotes: Bhagavatam's other verses such as 5.25.2, 5.20.38 and 5.16.4 etc. are related verses to understand this in more clarity.
