Can anyone recommend a thinner HDMI cable that is meant for in-wall use. I"ve bought a couple off of amazon now and they're all very thick. I'm wondering if anyone can recommend something. Thanks.
Try looking at Blue Jeans Cables. They have a thin product that goes up to 25 feet and a thicker product that goes much longer. The thin one "Series FE" is only rated at high speed up to 15 feet. The Series-1 is rated at high speed upto 25 feet and is more appropriate for in wall installation.
25 foot HDMI cables take careful mouth holding and the best approach is to make the cable with thicker conductors and thicker insulation.
You may want a cable with active line extenders, add an active cable extender you obtain yourself, or set up a system that is based on network cable (CAT 5E or CAT 6) extenders.
Mono price makes some good ones. Be very careful about using large diameter hdmi cables. The weight combined with the general low degree of flexibility (tight radius bends) will eventually break something, either the cable end or the receiver port. I have used 3 of the 75 footers. The first 2 were big diameter. Both broke at the end because of the tight bend going into the receiver. The little 90 degree adapters did not work in my setup. In about 2 years the two cables managed to destroy the port in my receiver because of the lateral loads placed on the port by the rigid cable. I was using cable restraints too. I ended up with a new receiver and one of the slim hdmi cables from mono price. Much lighter, much more flexible, just easier all around. I have not had any issues with the 75' length of run so it would seem excessive to use cat6 or other extender options for only 25'.