Plain-language search for an outdoor gear shop

Your company runs an online shop for outdoor gear with 40,000 products. Each product has a category, a price, sizes, an age group and features such as waterproof. Today search only matches words in product names. A search like "warm jacket for a 6 year old under $60" finds nothing useful.

A hosted model can turn such a sentence into filters: kids' jackets, size 6, insulated, under $60. Half of its calls finish within 400 ms, 9 in 10 within 600 ms, and 1 in 50 take over 2 seconds.

The shop gets about 500,000 searches a day, up to 30 a second in the evening. About 70% are 1 or 2 words, such as "tent". Results must appear within 1 second of pressing Enter. Today's keyword search answers in about 100 ms.

When does a search use the model, and what does the shopper see when the model is slow or down?