Some children can sit upright very well at six months. Mine couldn't so a solid, sturdy chair with a back and two sides was essential. At nine months Otis could use his chair independently, he could get in/out/up and down.
The child doesn't need to use the chair for weaning, it also makes a great place to sit and work. Here is a round up of some chairs available in the US, UK, New Zealand and Australia.
1. Me-Do-It Chair by Community Playthings in the US. They also have a UK site with a nice blog. We purchased our chair in Australia though Wonderland Rehab & Child Care Products found through FAS Therapeutic Equipment. The chair comes in 5" and 6 1/2".
2. First Chair by Michael Olaf. Michael Olaf is a highly respected supplier of Montessori materials based in the US. If you haven't visited their site before please do, it's essential reading for anyone interested in Montessori.
3. Infant/toddler "weaning" Chair by the Lord Company based in the US.
4. Chairries Chair by Jonti-Craft. This chair is available in a variety of heights starting at 5". It is available from a couple of online retailers in the US.
5. Poppet Infant Chair by Grocare available in Australia and New Zealand. I love the curve, it looks really modern.
6. Wooden Toddlers Chair by fastindustries on Etsy (based in the US) which at 8" is a little high for an infant, but have a look at their Wooden Infant Weaning Table and Chair Set, the chair featured in this set is 6" high.
8. Handcrafted Cube Chair from Montessori Child in Australia.
Cube chairs have the advantage of two seat heights and the chair can also be used as a stool or small table. Just flip the chair over. I love the look when two chairs are used together.
Some suppliers sell chairs specifically for the childcare and school market. If you are unsure about retail sales or individual pricing I suggest a friendly email or telephone call.
If you have a woodworker in your family these chairs will provide inspiration for a handmade chair. Wouldn't that be nice!
Please feel free to forward this to friends or anyone looking for a chair or leave a link in the comments to chairs that I have missed.