You are "allowed" to do whatever you want. If you wanted to drink a 10 pack of lager, wrap the baby in a snowsuit and put it under the duvet it's not illegal. I wouldn't recommend it but you could!
What you have been told is not current guidance. It's considered best to give parents information and let them make the decision they feel is best.
What you should know is that it is safest for babies to sleep on their own in a cot feet to foot. Unfortunately as you've found babies don't always agree that it's best.
Swaddling isn't against current guidance but becomes unsafe once babies start to roll, so be aware of that. You shouldn't swaddle and bedshare, it's thought to be an unsafe combination, but it's OK to swaddle if they're in their own space.
Sleepyheads are a bit controversial at the moment because they contravene "firm, flat surface", yet claim to be safe and breathable. The problem is that breathable doesn't have any legal standard associated with it, it's a completely unregulated term. No babies have died in sleepyheads but they are also not proven to be safe. You can make your own judgement here, but make sure to follow the instructions, especially guidance about when baby starts to roll.
The next to me crib counts as a separate bed whether the side is down or not. Again it's important to read and follow the instructions but these products are considered safe and do follow strict regulations.
If you choose to co-sleep with the baby in the adult bed you need to be aware an adult bed is not designed with a baby's safety in mind so the safety is yours to ascertain.
- Baby still needs a firm flat surface (never fall asleep on a chair, sofa, waterbed, etc or have them on top of pillows/duvet)
- Soft/loose coverings to be kept away from their face
- Make sure they can't roll out or into any gaps
- All adults in the bed need to be aware, sober, non-smokers, no children, no pets.
- Dress the baby lightly so they are not restricted in movement and don't overheat.
Co-sleeping following these guidelines is MUCH SAFER than unsafe, unplanned co-sleeping which is what happens out of desperation when parents feel shamed by health professionals. Some studies even show it is as safe as cot sleeping, but we don't really have enough data on this to be sure.
You can never eliminate all risk with whatever you do so it's about feeling comfortable with what you decide.
Good luck!