Make the cage one level before climbing becomes a fall
A one-level layout is the home adjustment that protects an elderly Campbell's dwarf hamster most, because this tiny species climbs enthusiastically long after its grip and balance have faded. Remove ramps, tubes to upper levels, and high platforms, and bring the wheel, hide, food, and water down onto the floor of the enclosure where a stumble means centimetres, not a drop.
Keep a wheel only if it is solid-surfaced, the right size for a dwarf, and easy to step into. A Campbell's who struggles to mount the wheel or is thrown by its spin is telling you it is time for the wheel to go and for exercise to mean floor-level wandering instead.
Water and food within a short walk of the nest
Low, nearby water keeps an elderly Campbell's dwarf hamster drinking without effort: hang the bottle so its spout sits at his standing height, or add a small, heavy, shallow dish he cannot tip or fall into. An older dwarf who must rear up and stretch for every drink will quietly drink less.
Scatter part of his food in the bedding near the nest as well as filling his bowl. Foraging is a Campbell's natural way of eating, and scattering close to home lets a stiff senior keep that behaviour without long, tiring searches across the whole cage floor.
Bedding deep enough to burrow, soft enough to sleep long
Deep, soft bedding supports an elderly Campbell's dwarf hamster through the long sleeps of old age. Give him enough depth to build a proper nest burrow, keep his chosen sleeping corner undisturbed when you spot-clean, and replace bedding in sections rather than stripping the whole cage, so his scent and his nest survive every clean.
Choose the warm, quiet room position carefully too. A senior dwarf's cage should sit away from draughts, direct sun, and the vibration of doors and appliances, because broken sleep costs a very old, very small animal more than it costs a young one.
Handling and health checks at his level
Gentle, low handling suits an elderly Campbell's dwarf hamster better than being lifted high for checks. Let him walk onto your hand or into a small cup at floor level, look him over there — eyes, teeth visible when he yawns or eats, coat, and how steadily he walks — and set him back down before he becomes restless.
Weigh him weekly in that same cup on a small scale. A Campbell's is so light that change shows in tiny numbers, and a steady written record catches a drift that fingers never would through his winter coat.
When home comfort is not enough
Contact a vet familiar with small mammals if an elderly Campbell's stops eating, develops a wet or dirty rear end, breathes audibly, or becomes wobbly and unable to right himself. In a dwarf hamster these changes can move fast, and the same day is the right timescale for advice.
Keep a simple log of the adjustments you made, his weights, and his nightly activity. Storing that log in KinsLe's Pet Passport means a vet seeing this tiny patient gets a real history instead of a guess, which matters enormously at his size.