htaccess mod rewrite with optional slash
===

We're switching from an old site to a new site with better URLs for SEO.
I'm trying to do this:

RewriteRule ^products/boots/materialid/(.*)/colour/(.*)$ http://www.mydomain.com/boots/$2/$1 [R=301,L]

However the problem is:

1) Instead of using (.*), can I specify that this can have the following characters
- any alphanumeric character a-zA-Z0-9
- any Euro character such as German special UTF8 characters
- _ and - symbols
- also can contain a + symbol (e.g. black+leather)

2) If the above won't work, and for my general knowledge on this, how do I update the above so that a trailing slash is optional? E.g. for the above rule, going to
www.mydomain.com/materialid/leather/colour/blue/
sends me to
www.mydomain.com/blue//leather
The extra slash comes because of the slash after "blue" in the original URL, but I need to exclude this.

Many thanks!