"If you go for spousal maintenance then I don't think it will be a clean break divorce - which could mean that if his luck changes and he end up without an income and you win the lottery/come into some money/secure a higher income he can seek maintenance from you instead!"
That's not true, it is a clean break... for you but not for him ;-)
If your luck changes, and you end up better off, the worst thing that could happen is for spousal maintenance to be reduced to 50p (yes, £0.50) a year and once you need it again you can re activate it (as long as you are within the period specified by court, I understand that most spousal maintenances granted are on "until wife re marries or 6 months cohabitation" rule).
If your needs are increased (or he becomes more wealthy), you can go back to court for an increase in spousal maintenance. Whether that is granted or not depends on how big and reasonable are your needs and how affordable that is for your ex.
Having said, spousal maintenance is becoming a rarity, you need to demonstrate the need for it, that he can pay it, and it will help if you can show that, had you not been supporting his career and raising his children, you wouldn't have ended up so disadvantaged in financial terms.
However, managing to convince a court of all the above could be a rather expensive business, you may need to spend thousands of pounds to get it, and it may take several years for you to recover that money from spousal maintenance payments.