Increasing the range of responsive image sizes made available in a srcset

PageSpeed is telling me (https://gtmetrix.com/reports/theemeraldemporium.co/xOPsfXpn) that I can acheive a 636KB saving by serving scaled images, viz:

The following images are resized in HTML or CSS. Serving scaled images could save 636.6KiB (71% reduction).

https://i0.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/002981.jpg?resize=450%2C450 is resized in HTML or CSS from 450×450 to 222×222. Serving a scaled image could save 33.2KiB (75% reduction).
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These images seem to be coming from product pages generated by WooCommerce (e.g. https://theemeraldemporium.co/product-category/emeralds/single/) which includes code such as:

<img width="224"
height="224"
src="https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?zoom=1.5&resize=450%2C450"
class="attachment-shop_catalog size-shop_catalog wp-post-image"
alt="2988 IMG_8076"
srcset="https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=80%2C80 80w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=36%2C36 36w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=180%2C180 180w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=120%2C120 120w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=450%2C450 450w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?zoom=2&resize=450%2C450 900w,
https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?zoom=3&resize=450%2C450 1350w"
sizes="(max-width: 450px) 100vw, 450px"
src-orig="https://i2.wp.com/theemeraldemporium.co/wp-content/uploads/2016/06/2988-IMG_8076.jpg?resize=450%2C450"
scale="1.5">

I can see that the WooCommerce catalog size default is set to 450×450, but in the srcset there seem to be other options available as well.

I suppose I /could/ change the WooCommerce catalog size to, say, 250×250, but is seems rather limiting for anyone with a bigger screen. Is there instead a better way of telling WordPress (WooCommerce?) to generate some other sizes and include those in the srcset?