I prefer the step-in harnessess for my two big beautiful yorks. At 13 and 16 lbs they can really pull and the step ins seem to be the safest and easiest to take on/off.
Chattiesmom makes beautiful harnessess and will make them a little wider for our plus size babies. They are fully adjustable, any I've bought can quickly be adjusted to fit either of my two, and have been used for fosters as well.
Target (believe it or not) occasionally has nylon step-in harnessess in the dollar bin.
I couldn't believe a harness for a $1, but now we stock up whenever they have them. They've proven very reliable.
My absolute favorite (although not a step-in) is the udogu harness.
UDogU These are soooooo easy to get off an on, wash beautifully and wear well for years!
Good luck!