Thimo Grauerholz

This plugin uses the Spreadshirt API to display the contents of your Spreadshirt Shop or Spreadshop via Spreadshirts’ API. It is made for SEO compatibility, so each article has its unique URL and uses Google structured data.
The basket is api-driven, so until you or the customer clicks checkout the customer stays on your website. Only after clicking the checkout button the customer is redirected to the basket of your Spreadshirt Shop / Spreadshop. The whole payment and order process is handled by Spreadshirt.
Using the plugin is quite easy! 
You only need to fill the settings, add the shortcode <code>[spreadplugin]</code> to a new or existing page or post, click <code>Rebuild Cache</code> and your shop is ready!
Current features 
* Compatible with old and new partner area (api) of Spreadshirt 
* Uses Spreadshirts’ own basket 
* Designer Sketchomat already integrated to allow customers to customize your products (optional) 
* Own product pages with custom URLs (SEO) 
* Basket Widget 
* Enhanced filter with extended shortcodes 
* Choose color and sizes 
* Multi-Language support 
* Social buttons 
* Enhanced zoom 
* Infinity Scrolling 
* Unique canonical, title, meta description with enabled Yoast SEO and Rank Math 
and many more…
What do you need
<ul>
<li>WordPress</li>
<li>Spreadshirt shop</li>
</ul>
Demo
https://www.mommyshirt.com/tshirts-fuer-frauen/
<h3>Known Bugs</h3>
<ul>
<li>If using W3TC, please disable page cache for shop pages.</li>
</ul>

WP-Spreadplugin

This plugin uses the Spreadshirt API to list articles and let your customers order articles of your Spreadshirt shop using Spreadshirt order process.

Frank Bueltge

Insert your personal Shirtinator Creator wrapped into WordPress without any popup or iframe.
How it works:
Please visit <a href="http://bueltge.de/wp-shirtinator-creator-plugin/510/" title="Shirtinator" rel="nofollow ugc">the official website</a> for further details and the latest information on this plugin.
<h4>Pemises</h4>
<ul>
<li>PHP 5</li>
<li>PEAR-package XML/RPC library</li>
<li>720px min. width in the design</li>
</ul>
<h4>Acknowledgements</h4>
<ul>
<li>Thanks to <a href="http://www.fatcow.com/" title="Fat Cow" rel="nofollow ugc">Fat Cow</a> for the belarussian language files.</li>
</ul>

Shirtinator

Insert your personal Shirtinator Creator wrapped into WordPress without any popup or iframe.

WP-Spreadplugin vs Shirtinator