This is a tricky age for it. These are what I'd look at though none is perfect, they all have pros and cons.
When you're going for a cheap/basic seat, rear facing is a very good way to achieve safety because all rear facing seats offer good safety even if they are extremely basic, whereas forward facing seats benefit much more from additional safety features, which you tend not to find on travel type seats because they add cost, bulk and/or weight.
The actually portable ones:
TinySeats - rear facing + isofix but expensive
Maxi Cosi Nomad - cheap, portable and good brand but has potential fitting issues and forward facing.
Nachfolger - rear facing, inflatable, good safety but hard to get hold of, expensive.
"Real" seats which are a bit lighter than average:
Graco Extend R129
Graco Slimfit R129
Joie Stages - all three of these above allow rear facing, belt fitted.
Cozy n Safe Fitzroy - RF to 13kg, FF to 18kg, cheaper.
Joie Elevate/Elevate R129 - forward facing only but lighter, belt fitted.
Cozy n Safe Hudson - 25kg harness but needs top tether
And controversial mention for the ultra-cheap "123" type seats sold in supermarkets/Asda produced by nania/team tex.
Because - they are extremely lightweight, cheap, available all over Europe in supermarkets, and if fitted correctly (watch the "Rear Facing Toddlers" video on how to fit a 123 seat on youtube) they are very universal, whereas some of the other belt-fitted seats (Maxi Cosi Nomad, Urban Kanga, Joie Elevate) you'll get a loose fit in cars where the belts are positioned too far forward.
However - these are extremely basic seats in terms of safety features, they are fairly flimsy and can get damaged easily, the crash protection on them is minimal, particularly for side impacts, they sometimes don't fit children well at the start or end of the age/weight bracket, and the instructions are very poorly written leading to a lot of incorrect use. But used correctly, they are definitely better than nothing and in fact the ADAC scores on them are "satisfactory". For a two year old, it's an option which is why I included it.