There are lots of different ways you can switch up your laps to make them less boring - but some of my advice will depend on your ability to perform alternate strokes at speed.
One of my favorite one plus mile swims is thus - you need to have yourself set up with leg buoy and kick board at your lane.
Swim 300 yards freestyle, then grab the kick board and kick 100 yards, then swap to the leg buoy and do 100 yard arms only. Do not stop in between, only long enough to switch from kick to pull aid.
Rest one minute.
Swim 200 yards breast-stroke, then grab the kick board and do 100 yards breast kick, then grab the leg buoy and do 100 yards arms only. Arms only breast stroke is not the easiest, so do your best to use good form.
Rest one minute.
Swim 100 yards backstroke, then do 100 yards kick only on your back (no kick board needed), then leg buoy 100 yard arms only. Back stroke is my least favorite so I do the shortest here, if you like back stroke but hate breast, switch these two.
Rest one minute.
Now go back to the breast regimen, rest one minute, and then repeat the freestyle regimen.
All told you swim 500+400+300+400+500 = 2100 yards, or about 1 1/4 miles.
You could also do this routine all freestyle, or anything else. The nice part of it is is works on your arms only stroke which should be helpful for tri-day because you ideally want to save your legs for the bike and run if you can.
Another workout I do is switch from free to breast to back every 200 yards, do that circuit 3 times and you are done with one mile. While you would rarely, or never use a breast or backstroke in competition, it helps to work your whole body, and keeps things different. Use these once a week to ward off boredom.
If you are looking to add speed, then you need to get into serious interval speed training. But on your "slow days" you can try these to keep things different.