There are lots - but I think IIRC you have mobility issues, are they relevant with this purchase? Or is the no isofix due to having an older car without isofix?
Do you have a budget at all? You might be looking at anything from about £90 to £500 depending on the features of the seat, special offers etc.
The ones which say one recline when rear facing, usually they can be fitted either forward or rear facing, they tend to have to be on full recline rear facing, whereas forward facing you'll have about 3 or so recline positions.
It used to be you could have seats from birth (Group 0+/1) or they would be from 9 months ish (Group 1/2). This has changed now.
The difference now with RF seats, is that they are either from birth (40cm) or from 60cm which is often given as 3 months - in reality baby needs to be able to hold their head up a bit and cope with less than a full recline, so if a seat is from 60cm, then it's from 4-6 months.
Then there are still a couple on the market which are old regulation Group 1/2 so from 9 months. Or old regulation Group 0+/1 which are supposedly from birth but don't always offer great support for a newborn.
It may be easiest to start off with an infant carrier, it's for your granddaughter isn't it? So DD may have her own infant carrier which ought to be easy enough to transfer into your car when needed (she should just make sure she doesn't get one which is isofix only). Then you don't need to worry so much what age your car seat is from, as long as it's ERF.