Current limiting required for float charge?
How much money and time are you willing to put into this?  I had a similar problem and I solved it with a Deltran Battery Tender from Powerwerx.
Five amp charger:  https://powerwerx.com/battery-tender-0220186gdlwh-power-battery-charger
A cheaper 3/4 amp charger: https://powerwerx.com/battery-tender-0220192-junior-battery-charger
Not a paid endorsement, just a happy customer.  Just make sure that the charger is big enough to provide enough current for the load as well as have enough to top off the battery.  I have both of the models I linked to above, the small one was insufficient to keep up with the load I had so I bought the bigger one.  The small 3/4 amp charger I then used to replace a broken charger for my electric weed trimmer.