My eldest was 30 months and walking everywhere so I just got a big pram, but as soon as the baby came my toddler decided to regress and would either try to run off/not walk holding the pram etc, or would decide they were tired and refuse to walk. So very early on I found it was easier to carry my baby in the sling and put my toddler in the stroller . This worked well and by the time the toddler was 3 they were walking everywhere again, but by then I was in love with my wraps so continued to carry the baby and didn't bother with a pram lol.
This time I'm not buying a pram (kids are older now at 9 and 11 and I sold the prams and strollers ages ago).
If I had a toddler though I wouldn't bother with a double pram, just stick to slings for the baby and a stroller or light-weight buggy for the toddler.
If you have a stroller/buggy that is suitable from birth, you can always get a sling and alternate them too (either carry the baby and push the toddler, or if the toddler is wanting to get out and walk the baby could then go in the buggy for a bit).
Also, I even back-carried my youngest until she was 3, so that would be another option for you.