https://www.homedepot.com/b/Outdoors-Patio-Furniture-Hammocks-Hammock-Stands/Chair/N-5yc1vZbxb8Z1z17mfj

The more you spread out the weight the better. BUT if it's only for a chair...then I wouldn't even begin to worry about this.

As I said...work men are able to walk across single trusses without 'damaging' the structure or loading. Therefore YOU 'sitting in a chair' is the same 'live load' for the area.

I WOULD do as you initially planned and span 4-5 trusses...use a beam calculator to determine the amount of deflection you'll get at each distance and use spacers/shims so you get equal loading to each beam. I'm 220# and walk across standard roof trusses with wild abandon...on one foot supporting all my loading. As I suspect you're equally heavy - and adding for chair and support you still probably wouldn't break a truss...but swing loading is different than static loading. So yeah...span 4 trusses have the outside trusses with like 1/2" spacers and the two closer ones with 1/4" spacers - that'll help spread out the load. As it's a chair it's presumed you wouldn't be loading it at the same time workers are also 'up there' (either roof or attic). Edit: Actually use a beam calculator to determine the correct deflection distances from the load - don't just run with the 1/2 - 1/4 I plucked out of no where. The closer you position to other vertical members the better - as everything 'works together' as a system.

Of course a hammock stand to the floor would 'spread out' the weight better...as that's got plywood as a load distributor instead of drywall - so you get more spread out loading instead of point loading.

I suspected it was a hammock chair...but it's more fun to be 'kinky' about it...but have also heard silly things like someone wanting to suspend fish tanks because 'it would look cool' - without realizing how much a lot of water actually weighs (and bodies being mostly water).

Anywhere you can spread out the load and transfer it more evenly to the ground is ideal.

I still would consult an engineer...only because were you to damage the home...or structurally impact it you'd need to declare (full disclosure) that in a home sale and/or insurance claim. Stamped calcs would clear you of 'reckless damage' (and other legal/financial risks).

As I said another option would be to stiffen up the existing trusses...usually done with slapping 3/4" ply on either side and through bolting (sandwiching the member). Stiffening won't 'solve' all the problems but will help transfer the loads to the walls and limit deflection.

Common safety factor is 2x and always plan for the worst...ala the potential of two people climbing in...the nicer thing about a stand is it becomes the sacrificial lamb instead of your ceiling/roof structure. You're unlikely going to cave in a floor any more than you would when two people hug/stand in the same spot.

Still engineering calcs would solve a lot of problems. I'd call one and find out the fee for it - it may be way less than you're suspecting - and determine how best to proceed. If the calcs cost more than a stand, get a stand...or if that would ruin your aesthetic and/or not fit in the ceiling height.

Giving up isn't a 'solution'...impossible only happens when you give up. You've got this...some things are worth the effort. Good luck and you're welcome.

Edit: I was the one that suggested transferring loading to the floor btw.