Great photos otterbaby, they are really helpful for explaining.
OP - the best time for a sidecar cot is pre-6 months with cot matress on highest setting (when everyone else is using a next2me crib). It gets a whole load trickier once baby can sit up, because of needing to lower cot matress height so sides are higher. Three options here.
- Lower cot matress so that you are now reaching down into the cot, rather than baby being at same height as you. Only works with solid sided bed (like a divan) that creates a barrier in the space below your bed matress.
- Furnature risers on the cot, as explained above.
- behave as if cosleeping. So don't leave baby unattended when awake. See below.
Once baby is crawling, as yours is, I think it gets easy again. Basically your sidecar cot just becomes an extension to your bed, but is equally an independant space. The difference between a crawling baby and a sitting baby (which needs the hassle described above) is motor skill developments.
As you have found, climbing very quickly follows crawling. Right from crawling you can teach baby to safely climb off the bed (crawl backwards to edge, dangle feet over while holding torso on bed, dangle and drop). They get it really quickly and loads of places to practice - stairs and sofa most obvious).
So once baby can safely get off the bed, treat the sidecar cot as if cosleeping, but independant cosleeping. So don't leave baby in the cot alone when awake, stay close by as going to sleep (even if you're just lying at opposite side of your bed as baby drops off to sleep). Then once asleep, no need to worry about climbing and baby can't roll out of the cot. If/when baby wakes, try to get to baby quickly but if you don't manage to, baby has the skills now to safely get off the bed unaided.