OP perhaps citizens' advice can help you find out what arrangements for your husband's care you can put in place to come into being if you should go before he does.
I unfortunately cannot help as I don't live in the UK.
Your GP might be the person to discuss this with too.
Basically, I assume that if your husband is mentally competent but physically disabled, it will be up to him to make arrangements for his own care, but as I say, I don't know.
Certainly, someone apart from yourself should have a power of attorney, or be joined with you in one to obviate the risk of there not being anyone legally entitled to put arrangements in place.
Perhaps the paid carer you mentioned can put you in touch with the proper authority you need to deal with.
Here in Denmark, we can make arrangements with an undertaker, lodging details of the funeral we want and even paying in advance, although most people leave the payment to be dealt with by their estate. Here wishes regarding the funeral that are included in a person's will must by law be respected, but I don't believe this is the case in Britain. It might be worth your while to speak to an reputable firm of undertakers, because although the funeral arrangements are less worrying than your husband's care, knowing they are sorted will give you peace of mind.
A solicitor should be able to help, but of course will want a fee for doing so. Your bank manager has experience of the ins and outs of dealing with someone's estate and may have come across this particular problem before. It can't do any harm to ask.
I think it is very wise of you to try and safeguard your husband's care, should anything happen to you, so I hope you find someone who can help you with all this.