There is no 0/1 FF only, if you want a 0/1 then it will be RF and FF, because Group 0 is always rear facing.
If your little one is over 9kg and you won't ever use the RF function of a 0/1 seat, then you might as well just get a group 1 unless you happen to find a 0/1 cheaper. Beware of the ubercheap 0/1s though! There are a lot of crap ones on the market. I'd only trust Joie and Britax at these price points. I doubt you'd get any other brand cheaper. I'm not even sure about the own brand car seats any more, so probably just avoid them.
The Tilt is always going to be cheaper than the Steadi, so you can rule the Steadi out on price. The only difference is it's more padded.
The First Class and the Eclipse you might want to look at and possibly try out just because the First Class has such huge discounts ATM. IIRC both of these are recommended for cars with short seatbelts because they both have two belt routings (First Class only in FF mode). I used to have a First Class for DS back when proper ERF was out of sight for most people and I really liked it.
The Eclipse is Britax's most basic seat but it does the job.
Then I'd probably check the Evolva - it's big so that might be a fit issue (they should have a fit finder on their site) but actually it might be alright for a 1yo. I'd look on the offchance but not expect too much.
I would fit the seats for your mum (assuming she'll have them in all the time) and make sure you kneel your weight into the car seat at every stage when you tighten the belts. IME this gives an absolute rock solid fit (I've done it personally with the Eclipse and First Class, not seen the Joies IRL) and the seats should not move around. So if you're looking for usability for your mum I'd look for things like the straps being easy to adjust/tighten and if there's a recline, that it's easy to use without changing the fitting of the seat itself.
Check Britax and Joie's website and their fit finders, then you can rule out any which you see won't fit, but even if they all fit, this is only 3-4 to look at in total.
Mothercare price match their website so ask if the price is higher in store. Sometimes you can get discounts this way.