So we started by bunking a Kura Ikea bed that started as a floor bed-- also bolting on an ikea Trofast staired storage in lieu of a ladder, adding climbing holds, and eventually turning the largest compartment into a hanger space for clothes. Beyond feeling a little anxious about putting a barely-walker up there with all the safety labels about her needing to be 6, this worked ok in the diapers overnight phase.
Once she was flat out refusing to wear pull ups, we had some success getting her to just move from a wet upper bunk into a dry lower bunk. However, as our aging dog started having incontinence issues and our unneutered dog felt this was the perfect environment to lift his leg around, I started to doubt whether the lower bunk was acceptably clean between weekly sheet washings. I also found that the big fluffy duvet covers took up a ton of space and unbalanced the washing machine which would start hopping around the laundry area with its midnight load.
So we swapped bulky duvets for 2 lands end cozy plush fleece throws on sale for $13 each. I also found after repeated washings, the waterproof/resistant mattress protector on the main mattress soaked completely through. Lots of baking soda, vinegar, and sun treatment with vacuuming for that mattress to control the damage. Given the incontinent dog, I had large up&up dog pads on hand and started sticking one of those between the mattress and the mattress protectors, just in case.
So here is our current set up: mattress+dog pad+emergency sheet+dog pad+mattress protector+normal sheet+fleece blanket. I clip the mattress protector, normal sheet, and blanket together at the foot of the bed to easily pull it off if wet. I keep the backup fleece folded at the head of the bed (with hand towels because wet hair makes an unacceptable "splatter" on the pillow).
Stuff that still isn't great-- the dog marking situation. that she needs to have someone read to her until she is completely asleep. there are still a lot of stuffies and other stuff to move in the middle of the night (but putting them in a grandma beanbag poof keeps them out of the way). that she needs to have a goldfish snack in bed and then spills it and creates intractable grease stains on her sheets.
10/9 still bedwetting. Have discarded the clip system. Have added a second layer of lasagna, so now she could wet the bed 2x and still have somewhere dry to stay. Ordered Goodnites Moana and will see if she is willing to wear them.