I'm a BIG BIG BIG fan of 1x10 for MTB purposes.
Generally, going from 2x10 to 1x10 is a piece of cake. 3x10 to 1x10 can bring in the consideration of chain line, depending on what front chainring you want to use and if you're bike-vain like I am. Given that you have a Tiagra triple, your front crankset will probably be 130/74mm BCD... I think?
130mm BCD chainrings don't generally get smaller than 38T. 74mm BCD chainrings can be teeny weeny. What chainring are you planning on using?
It's easiest if you're just fitting the chainring to the middle position on your crankset. All you need are 1x chainring bolts and away you go. If you're vain like I am, then you'll want to put it on the outside position to cover up the ugly parts of the crankset, you'll need to faff about with spacers on your BB to get the chainline more in the middle.
In terms of a chain guide, for most road use you probably don't need much. But if you want to be secure, look at using a top-of-chainring style chain guide. To cheap out, you can use a FD as a chain guide. Alternatively, a nice slimline chainguide like the Paul Components Chain Keeper
is nice and streamlined (Works well on my MTB). There are other options like the E13 XCX and the MRP 1.X for XC MTBing. No personal experience there, so not sure if they'll handle the chainring size you're after.
There is also the Widgit
(which I've also used), but it's mostly for XC MTB use so I doubt it'll have a big enough chainring for you.
Also, consider a Wolftooth
chainring. It uses the wide/narrow style found on the new SRAM XX1, so doesn't need a chain guide and reviews are very very positive for it. Buuut you might need a different RD to provide more chain tension. I've just fitted one to my MTB and have yet to try it out. Looks hawwwwt though