Joie seats are absolutely fine! They are a bit more basic than some brands, and sometimes it's worth paying a bit more for comfort or practicality, but as far as safety goes, they are a very good way to achieve safety on a budget. They are miles above some of the very dubious online-only brands which are around.
For a 20 month old these are all the kinds of seat you could buy, starting with 2 that I'd probably recommend looking at first. Rear facing is probably the most important thing you can do safety-wise, for as long as possible, so both of the best fit options allow continued rear facing.
If you have an idea of direction from these descriptions then I'd be happy to go into further detail.
"Best fit" for most people:
Isofix spin seat - up to about "4 years", with base permanently attached e.g. Joie i-Pivot, Britax Dualfix, Cybex Sirona. They can be used rear facing usually all the way up to the 105cm/~18-20kg limit, or you can turn forward facing when you're ready. They don't have a lot of leg room for rear facing mode but they are a great compromise if you want to RF a bit longer but you know you don't want to stick with it long term, and/or if you are TTC again, so you'll be able to hand the seat to a younger sibling. Lasts until about age 4, but for a very big/tall child, possibly only about age 3.
Swedish type ERF - designed for more comfortable, long term rear facing up to approx 6/7 years max (you do not have to use them this long of course!) They do not face forwards. Yes some cost about £400 - but they start at about £200 and there are often offers around. They are usually worth considering if you're keen on the safety benefits of extended rear facing, because they're more compact in the car, have good leg room for older children and will last as long as you need regardless of whether you choose to switch to FF/booster seat at age 4/5/6+, so can save money, esp if you have a taller/heavier than average child and would need to buy an extended harness or extended RF seat long term anyway.
Seat types for 3 specific situations:
Dedicated FF seat - no booster - probably Britax Trifix 2, Cybex Anoris T or Britax King Pro (if it needs to be seatbelt fit). As said - not great to be FF at 20mo, but if that is your strong preference, then aim for a seat which is designed solely for this stage and isn't having to make compromises by accommodating the booster stage as well.
Budget RF seat - If you want to stay rear facing for the safety benefits but are on a tight budget, you might consider some of the belt fitted seats under £100 like Halfords Impala, Joie Stages, Graco Extend R129. There are some drawbacks in that the shell length tends to be short so you'll need another seat before age 4. They also can be awkward to use in terms of posting child over/under the seatbelt. But they are a good safe option if your budget is vv tight, you don't have your own car, or you need a spare/second seat for another caregiver. It is worth noting that Graco Turn2Me and the original Joie 360 Spin are often available for around £120 if you want/need to spend less but prefer the isofix/spin style.
Base compatible modular seat - if you already have an isofix base for your baby seat and there is a compatible toddler seat for it, sometimes this is worth buying if it has a feature you like (e.g. Besafe Beyond) or if it is on a good price offer. However, most of the time these are more expensive than but almost identical or slightly worse than the 360 spin base-attached model from the same brand, and it takes the base out of use if you want to sell your infant carrier or have another baby. So, usually a false economy.
Seat types to avoid:
Forward facing harness + booster combo - they tend not to be well designed for children this young, or sometimes fairly lacking in their overall safety. If on a budget stick with a budget RF seat, if FF is the priority, look at a dedicated harness/shield stage seat.
All stages "does everything" type seat - often poorly designed, difficult to use, restrictive (e.g. RF mode can only be on full recline), bulky, and/or expensive - a false economy. 10+ years is also a very long time to use one car seat. It's almost always cheaper and better to get a cheaper seat from the first 2 categories at around £150-200, then a basic or mid range high back booster, around £50-100. (A decent all-stages seat is about £350, the ones under £200 tend to be especially bad). People sometimes get on alright with them, but you'll get a better experience by specialising to the stage you're at, in general.