Best 123 reasonably priced but safe seat for 2nd &3rd car?

[Kri5ty]

I'm really paranoid about car seats. Ds is 2 and in an ERF.

We have ds2 arriving in may and need a seat 123 seat for ds1 , as a spare seat for grandparents (as he will be staying there when ds2 is born.)

Can't afford another ERF, and it needs to be belted/ easy to install for grandparents?!

[Kri5ty]

Or even just a group 1?

[Ihateparties]

Could you stretch to one of the joie seats? Stages or steadi, they both rf to 18kg although admittedly in a less ideal way than the top of the range seats.

[GoodEggSafetyAdvice]

Hi,

What car do the grandparents have?