Harness for 6-week-old Chihuahua mix

A 6-week-old Chihuahua mix is genuinely at the tricky edge of what harnesses are designed for — most 'extra small' sizes are still built for dogs a few months older and a good bit heavier, so you're right to question whether anything off the shelf will actually fit safely right now. Small dog harnesses already have specific fitting challenges — most gap too much around the chest or are too structured for tiny, still-developing bodies — and a Chihuahua mix at this age adds another layer to that. To point you in the right direction: roughly how much does your pup weigh at the moment, what's the mix if you know it, and are you looking to use this for short outdoor trips or just getting them used to wearing something?

600 grams is very small — you're right that most harnesses won't fit yet, but the good news is that at this stage you're really just doing habituation work, not load-bearing walking, so you don't need anything heavy-duty. What's the rough chest circumference if you've measured it, or even a rough guess? And is she generally calm being handled, or a bit wriggly?

That's really helpful. For a wriggly pup at that weight who's purely in the 'get used to it' phase, I'd go with the Puppia Soft Harness in XXS. It's a vest-style harness in a breathable mesh that sits around the chest rather than putting pressure on the neck or spine, which matters a lot for a puppy this young whose bones are still forming. The XXS fits chest circumferences from roughly 17 to 21 cm, so she may just about be at the lower edge now or reach it within the next week or two — worth measuring around the widest part of her ribcage before ordering. Because it slips over the head and fastens with a single chest clip rather than lots of buckles, it's much easier to put on a wriggly dog, and the soft mesh means she can wear it for short supervised sessions without any chafing. It's widely available on Amazon UK and well under £15. You're not walking her on it yet — just letting her wear it indoors for a few minutes at a time so it's normal by the time she's ready for the outside world.

Short supervised sessions in a well-fitted soft harness won't cause any developmental harm — the key words there are well-fitted and short. What you want to avoid at this age is anything that puts sustained pressure on the spine or restricts shoulder movement, which is why a vest-style like the Puppia works better than a figure-of-eight or a rigid H-harness for a puppy this small. Keep sessions to five or ten minutes, don't clip a lead to it yet, and check that you can easily slide two fingers under every part of it. As she grows — and Chihuahua mixes grow fast in the first few months — re-check the fit every week or two. She'll probably move into an XS within a month or so.

Great plan. Measure around the widest part of her ribcage — just behind her front legs — and if she's below 17 cm, give it another week before ordering rather than forcing a fit. The habituation work you're doing now really does make a difference later, so it's worth taking your time with it. Good luck with her — Chihuahua-Pom mixes are brilliant little dogs.