I like a knot called a "Slim Beauty" instead of double Uni. Way smaller IMO. We use this knot for fishing inshore and offshore to tie our mono or fluoro leader to braid. I also like this for ice fishing as I hate seeing my swivel on the depth finder. This knot passes easily through the guides. Simple description follows:
1) Tie figure eight knot (you can tie this directly, or you can tie a double granny/double overhand in mono and pull it until it flips into a figure 8, leave it open enough to pass braid through.
2) Run braid in same direction through figure 8 where mono exits.
3) Wrap braid 10-20 times around mono (experiment with number that works with the pound test you are using) and then pass braid back through figure 8 knot in same direction you came through originally.
4) Cinch figure eight knot tight.
5)Pull on both parts of the braid until knot is cinched.
6) If you did it wrong it will slip out.
7) trim tags close.
Here is a link that does a reasonable job, except they do not run back through the figure 8:
https://www.youtube.com/watch?v=Fnm7MffdkjcNote most links you find on youtube are for very heavy offshore applications and include doubling the braid before going through the figure 8. You do NOT need to double the braid IMO. Most links also do not pass back through the figure 8 but I find that to be an exceptional knot.