A). Universal Basic Income. It would help stop people falling through the cracks. Additionally studies show it doesn't disincentive work but actually does the opposite and helps people get into and stay in work.
Also, there's currently fewer total job vacancies in the UK (916,00) than job seekers (over 1 million), and that's not even including people on sickness benefits).
B) Improve the NHS. Quicker waiting lists and better early diagnosis and referral system (I know several people with physical health issues that were originally misdiagnosed as mental health problems).
C) Better social care system with proper investment and effective supportive help.
D) Incentives or legislation to encourage businesses into employing and retaining sick and disabled people.
D) Benefits system that provides sufficiently and is empathetic. Punitive systems make people more ill and less able to work. Also recognise the value of carers (who save social services a lot of money).
E). More social homes (including more disability friendly and accessible homes), and end RTB.
F). Return state pension age to 65. Life expectancy might've increased (although I think that's no longer the case?) but many people's health isn't good enough to keep working. Also young people won't be able to get jobs if older people aren't retiring.