My partner and I have started using a lube syringe before sex. It’s actually an old injector for children’s liquid tylenol. 
But we’ve found that using a syringe allows us to get it in deeper, so then it kind of releases more slowly and allows us to go for longer before needing to add more.
What do you all think? Do you use any sort of applicator for lube?
Make lube or vaseline ice cubes. Let him push 2 or 3 all the way in with his cock. They take time to melt inside you so release lube over a longer time. Basically never need to reapply.
(If you dont like the shape of normal ice cubes then google “pessary mold”)
I always use large syringe that my wife used to use for vaginal cream application. Perfect lube is thick gel of xanthan gum.
brrrr, sounds cold! But also hot. 
But seriously, I never would have thought of this idea.
For liquid lube I also use a syringe (no needle of course!). In the U.S. they syringe body can be purchased for any number of sources. They are also useful for craft projects, mouth feeding medicine to some pets, etc. Of course, maintaining hygiene is very important – be sure has been very thoroughly cleaned before putting into the source-jar for refilling.