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Thanks all, good ideas - I do have an expensive electric bed, which obviously I haven't been using very well (plus the fact that last week doing some experiments I managed to bust the motor mechanism!) - but the bottom of the bed still rises, so I'll play with that a bit and see if I can get that to lift me enough not to slip.
Bed engineer is coming next week to fit a new motor and charge a fortune (but my fault, so no real complaints).
(No Pixie, not entitled to anything! We have small industrial pensions on top of old-age pensions, which puts us in the 'no way' bracket when it comes to entitlements - not rich, but not poor enough...)
BB