When you say it's not compatible, is that because the fit list says no or can you not get a safe fit in that car? And if you can't get a safe fit, what's the problem exactly? TBH, Joie Bold would not be my choice of seat, because your DC is not on high centiles and it's more complicated to fit than most seats for this age/weight group, needing isofix, tether and seatbelt all at the same time.
Do you have access to isofix and top tether in all the cars you will be using it in? And do you definitely want forward facing, or would a rear facing seat also be OK?
When you're carrying it to the car it will be fitted in, does weight/bulk of the seat matter?
Do you currently have a seat for him - is this being passed to a sibling? (Sometimes it makes more sense to buy a new seat for the younger child)
And do you have a budget 
Without knowing the answer to any of the questions, I'd say that my general usual recommendation for a Group 123 type seat for a child with this height and weight would be Britax Evolvafix or Silver Cross Essentials Balance, because they're not too expensive, decent safety rating, good weight limit and are easy to use, with the only issue being that both of these seats need isofix and top tether for the harnessed mode - but all cars produced within the last 13 years have this, and most cars produced since about 2006 have it, so it's usually only a problem for vehicles aged 20+ years.
So if that is a no go, then I would probably look at Joie Every Stage R129 or Graco Slimfit R129 - it's seatbelt fitted so doesn't need isofix at any point, meets the newer safety standard, it's a rear facing seat up to 105cm/21kg (which will be about age 5 for your LO) and then after this, or from minimum 100cm (which will be about age 4 or a bit older for your LO) it turns around to use as a high back booster seat. As it's rear facing, it wins in the safety stakes even over an isofix forward facing seat, but some people are less keen on RF by nearly 3.
As said - with more info I might make different recommendations, but that's what I'd say off the top of my head with the info given here so far.