hmmm! I like to spend some time looking at a lot of videos of the species if they exist, particularly veterinary videos (like from a reputable zoo or owner's social media) where humans are handling/next to the animal can help you get a practical understanding of the scale of each part of the body in relation to a base (of your own). A human's hand actually unfurling the wing of a barn owl does a lot more for me to rationalize scale than anything else. I find isolated photos (like a squirrel sitting on a fencepost) are the least helpful... even photos/videos of the animal cohabiting on a farm or in an enclosure (like say, some species of capybara and monkey housed together)-- even if it's not the animal you are imagining with them specifically-- will help create a general vividness to its scale in your mental library.

the more connections you make, the more footage absorbed over time, the easier it will be to add more species into your mind and run them around. At that point, you kind of play 6 degrees of separation with everything-- like-- "ohh it's THIS big next to a macaw, and I've seen a macaw next to a dutch rabbit, and this animal is roughly the size of a dutch rabbit, so..." <-or at least, enough of a working idea to feel confident bullshitting... (:

next thing I try to focus on to help constrain proportions, is INDIVIDUAL body parts in relation to one another... if you tell yourself, "the height of the cat to the shoulders is equivalent to this antelope's hoof-to-wrist", you can "check" yourself at any moment drawing. "The length of this donkey's ears should be the same as the cat's tail" "the horse's hoof should be about the same size as the bobcat's entire head"... "the sheep's back comes up to the draft horse's belly".... As you draw, you can then go "oh fuck, the hoof's WAY too big next to the tanuki's body, so I messed up the scale at some point"

of course just drawing a very flat, simplistic profile comparison of the two full bodies is always my first step. It helps to TAKE the drawings, put them on top of each other, flip them... I like using tiny simple pixels obviously, because I can really uhm drag them around the screen freely and see them in one very brief glance, gain the immediacy of silhouette. I don't feel detailed close-ups or high-res help processing at all, personally!

Obviously (probably), turning the bodies into very very basic shapes and then layering those shapes in different angles can help process. It helps to really EXCISE FROM THE MIND the general concept of a human skeleton, cranium, etc. A lot of animals have BIG RECTANGLE HEAD WITH SMALL BRAIN CASE, or BARREL BODY, so constructing them from cranium-ribs-pelvis like you often would a humanoid is no good, and you're better off treating the lioness's body as a big 3-dimensional rectangle.... and then just flipping a rectangle around, kind of as if you were drawing a couch.

as for posing specifically with a small male, it's really not unusual for young of any species to interact with older conspecifics, and this is good inspiration for how any creature deals with a much larger female! I watch a LOT of footage of baby/adolescent animals in particular because they are just so much more irresponsible with their bodies and tend to truly flop and tumble and twist themselves around littermates, get squished and sat on etc, which can be a valuable inspiration for the kind of intimacy one imagines with original characters! Adolescents often just FLING weight around and at things, much less precious about their stability, balance... I feel like, the dream is often sortof using something like, HOW lion cubs play but applying it TO something as crazy as an antelope, an animal that isn't usually crushing its body against another or laying belly-to-belly... what if a cape buffalo was as comfortable and lax with its anatomy as a bunch of ferrets in a pile? Again this is where just a greater, sheer amount of mental reference will aggregate .... and inform one another.