Is a firm mattress + latex topper a good idea?

I’m located in London, Ontario, Canada and shopping on a budget (5-600$ CAD). Looking for a queen for me and my partner. Wife is a side sleeper and I’m a combination sleeper. Both of us are average body weights. We will need the new mattress to last us 3 good years.

I would’ve ideally preferred to buy a latex mattress but money is a constraint. Do you guys think it will be a good idea to buy a firm mattress and top it up with a 2" latex topper?

Or if you have any good recommendations in my budget, please let me know.

This is similar to what I do. Actually I’ve had the same relatively low cost FIRM simmons beautyrest pocketed coils mattress for over 15 years! I put a topper on top, and the fee is just right, and I replace the toppers when worn out.
Since the spring of the Simmons are firm, and it was the highest level of firmness of the model, and so there is minimal built in comfort layer in the mattress itself, its just does not wear out! Unless one is going to have kids jumping up and down on the mattress , such firm springs really will last a long time. I have seen no reason to replace the actual mattress since it is as good as new to me. I use memory foam toppers on top, and find they will tend to start to wear down in 3-5 years, so my only cost is replacing the topper every 3-5 years, quite a low cost. I’ve been doing this for 15 years or so.
I use memory foam but you could do the same with latex topper, which may well last longer than memory foam does.
If you have different opinions between you and your partner, as far as the topper you each can have a different topper. Thats what I do - my and my wife have different Twin XL beds next to each other to make it essentially into a split-King. If everything is of similar height, with bedspread on it really looks like a King.