I second the model shop recommendation. I consider it to be one of the best shops in Switzerland, but it's not just "a short tram ride", it is also a fairly steep uphill walk. Also further up the hill is another good shop H & M Beltrami at Spalenvorstadt 22
 
Google  map showing both streets
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http://goo.gl/maps/4L7p
Here is the long standiong Swiss Railways Society directions to both shops:
 
Bercher und Sternlicht
Spalenberg 45

Basel station   20 mins walk, less by tram.
In Old Town. From SBB take Schiffkude tram to Marktplatz (about 1km walk). From SW corner of Marktplatz, runs Hutgasse which crosses another road and becomes Spalenberg. Shop has small frontage on left going up hill. Long and narrow shop on 2 floors
 
Beltrami:
Spalenvorstadt 22  
 from Bercher & Sternlicht (see above) Go up to the top and bear right, cross another road following the tram   shop is on the right. There is a tramway stop between the two shops. The road continues to the Spalentor.

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