Firstly, if you haven't done so already, I would simply recommend reading "The Travels of Marco Polo" as a wonderful and accessible approach to the topic.

"The Prehistory of the Silk Road" (2008) offers a good background to the numerous cultures within the Steppe of Central Asia through which the Silk Road passed and just how these peoples interacted with and helped birth this famous trade route.

Ibn Battuta was a famous 14th c. Islamic traveler and explorer whose journeys often included travel on the Silk Road, and although he was not a merchant himself, he often traveled with merchant caravans

"Empires of the Silk Road: A History of Central Eurasia from the Bronze Age to the Present" is a journey through the various Central Asian empires and retells the story of history from their perspective.

http://www.scribd.com/doc/9839252/Mongol-Empire-Silk-Road-and-Globalization This is a link to an article which looks up your alley, titled "Mongol Empire, Silk Road and Globalization". It would be an approach to the Silk Road via the Mongols, under whom the region of Central Asia and Silk Road trade flourished.

"Foreign Devils on the Silk Road" (1984) tells of late-19th and early-20th c. archaeologists who traveled the Silk Road across the desolate Taklamakan desert to Western China in search of remnants of ancient civilizations. Lots of good history on the Silk Road in there.

"Caravan to Lhasa: A Merchant of Katmandu in Traditional Tibet" (2011) by Kamal Ratna Tuladhar, in which he describes the caravan journey taken by Nepalese merchants from Katmandu across the Himalayas, through the lens of such journeys taken by his merchant father from the 1920s to the 1960s.

I would suggest beginning with Ibn Battutah's account. Polo's work is interesting, but the convoluted source tradition and anachronistic account makes the text's veracity dubious at best. For a discussion of these problems, see Frances Wood's Did Marco Polo Go to China for a discussion of this: http://www.worldcat.org/title/did-marco-polo-go-to-china/oclc/173318954&referer=brief_results

The travels of Ibn Battuta, on the other hand, are more easily believed. If you can read French or Arabic, the Hakluyt Society has an unabridged bilingual edition. If you're limited to English, I like the Mackintosh-Smith abridgment better than the Rev. Samuel Lee one:http://www.worldcat.org/title/travels-of-ibn-battutah/oclc/49394398&referer=brief_results. Additionally, I strongly suggest Ross Dunn's contextual work, which provides a brief social history of each or the regions that Ibn Battuta visited: http://www.worldcat.org/title/adventures-of-ibn-battuta-a-muslim-traveler-of-the-fourteenth-century/oclc/13329511&referer=brief_results.

It should be noted, that Ibn Battuta was not a merchant himself. His work is part of a tradition of "pilgrimage writings." The author was a Maliki Jurist who went on the Hajj and kept traveling. He did, however have close associations with Sufism, a religious movement whose lodges were often found on trade routes.

As far as European merchants, I would recommend Origo's biography of Frencesco Datini: http://www.worldcat.org/title/merchant-of-prato-francesco-di-marco-datini/oclc/27699999&referer=brief_results Datini was a mid level merchant with offices throughout the Mediterranean world. What is more, he saved all of his correspondence and records for posterity, which allows for detailed studies. Indeed, the city of Prato hosts an annual conference on economic history in his honor.

In terms of "big picture" accounts of the medieval world economy, Janet Abu-Lughod's Before European Hegemony is a bit dated, but still the gold standard on the subject: http://www.worldcat.org/title/before-european-hegemony-the-world-system-ad-1250-1350/oclc/18462916&referer=brief_results.

If you want an interesting primary resource, Pegolotti's Pratica della Mercatura describes the practice of merchants during the Middle Ages. A translation of the excerpt can be found here, https://depts.washington.edu/silkroad/texts/pegol.html and the entire edited text can be found here, http://www.medievalacademy.org/resource/resmgr/maa_books_online/evans_0024.htm#hd_ma0024_head_001. Even if you can't read Italian, the introduction is still worth a read.

If you want a unique mercantile group, Schlomo Goitein's multivolume analysis of the merchant communities whose records were preserved in the Cairo Genizah has been abridged into one volume: http://www.worldcat.org/title/mediterranean-society-an-abridgment-in-one-volume/oclc/40444152&referer=brief_results. Goitein's work is still well received, but Jessica Goldberg recently reassessed the Genizah community in her work Trade and Institutions in the Medieval Mediterranean. http://www.worldcat.org/title/trade-and-institutions-in-the-medieval-mediterranean-the-geniza-merchants-and-their-business-world/oclc/758099071&referer=brief_results. Given the price, you may want to order that one from the library. Its well worth the read, however, and the work has received glowing reviews from every scholar I've spoken to.