Are you familiar with the concept of a Multiverse? A Universe may be just one region of it, and I would think that various kinds of fields may exist that are larger than a single Universe. If a Universe is initially just a singularity it is contained within some volume. Parmenides and Heraclitus might have liked that kind of inquiry. There are different and scalar kinds of singularities just as some infinities are greater than others (re; Greg Cantor and trans-finite numbers).
If a Universe expands from a singularity that had all of the energy that would eventually become mass it is probable that some universes expanded from different sizes of singularity. Some black holes are larger than others.
You may be aware that mass and ‘objects’ are nothing more than apparent phenomena occurring in the Higgs field. Two-dimensional particles slow down in the field and pick up an appearance of a third dimension in the direction of travel. Massless two-dimensional particles seem to be close to the basic state of everything.
I would not guess the true state of Universes is simply singularity or mustard seeds that expand for a while into universes before spending all of their energy in thermodynamic processes. There may be more than that, yet I believe a singularity is a real object that is one and comprises an entire universe-in-itself. Some people prefer to call a Multiverse a ‘universe’ and that is reasonable I suppose. That reinforces the idea that none know what a Universe is well enough to set comprehensive boundaries.
Quine defined the concept of linguistic ‘universes’ rather well in Ontological Relativity. Each language lexicon is like a defined set of numbers that can’t be converted directly into a different set without corrupting the elements. The meaning of Universe exists in different lexicon/word sets and is part of the challenge of postulating metaphysics for cosmology, universes, Multiverse etc.
Information is conserved- Shannon Entropy, and isn’t destroyed. Apparently no information is lost; not even if the Universe ‘ends’. Matter and energy are convertible and were thought to be neither created or destroyed as well. That raises the point that if information is created yet not destroyed permanently (not even in black holes); was information never created (except by God) as well? Did the information of the Universe pre-exist the existence of the Universe? If determinism with free will is the fact the author of a deterministic Metaverse might not be required by anything he writes into being to rewrite it or ever be subject to the laws of a contingent universe. I believe it useful when considering metaphysics of universes to consider what God could do with universes to infer characteristics of singularity and universes for-themselves.