Hi Mightymouse - congratulations on your pregnancy!
I am also 40 and 6.5 weeks pregnant (grrrrrh you are 7 weeks, wish I was!).
The hyperemesis that I had with my first pregnancy (DS is 2) returned with a vengeance about a week ago. I have the same problem that I work for myself and won't make it much longer lying in a heap in my dirty tracksuit.
I cannot comment on your reactions to drugs so far. But I know that Cyclizine is the first drug recommended by most doctors for morning sickness. Totally proven to cause NO harm to your baby. For me it is not strong enough - doesn't touch the severe nausea and makes me very tired. You should try it though because as Dlah says above, it does work for many.
Ondansetron (American brand Zofran) is stronger, different sort of drug and most women DO achieve great results with it. If you don't achieve good results with Cyclizine very quickly, I wouldn't hesitate to move fast over to Ondansetron as that really should make a difference to you. You will see 100s women on the Hyperemesis Support thread swear by both its effectiveness and safety to baby.
I am lucky enough to have some private consultant advice andcare for my HG, and yesterday I went a step even further. I have just started a course of Prednisolone (steroids) for mine. There is a theory that severe MS is an inflammatory response of the immune system which can be suppressed. I have been entirely convinced that this is also safe for my baby (not least because 1000s women use Prednisolone during IVF treatment). I have not been sick since I took my first dose, my nausea is almost gone, and I am operating almost as normal at home. Just tired and still need to eat really regularly.
I just mention this to reassure you there that there are many options for you to to consider. The NHS is VERY stingy about prescribing Prednisolone for MS, so depending on your finances, if you really wanted to try it, you may need to find a friendly private GP to prescribe for you.
I hope this helps. Hyperemesis is the absolute PITS and reminds me why I swore I would never try to have another baby.